Spooky eyes on the Stygian rainforest floor: Headlight beetles, fire beetles, Pyrophorus spp.

 

Two whiteish patches on the pronotum of the headlight beetle contain specialized cells called photocytes. Reactions in the photocytes produce the beetle’s eerie greenish bioluminescence, reputed to be the brightest light in the insect world. Image: Paula M. Shrewsbury, UMD

 

Over the past several weeks we’ve escaped the freezing weather of the DMV and traveled to the steamy rainforests of Belize to visit busy stingless bees, fierce assassin bugs, and oversized, friendly tarantulas roaming the landscapes of the Mayans. But what could be more fun than a nighttime visit to the untamed rainforest at the Toucan Ridge Ecology and Education Center with the hope of glimpsing an ocelot or maybe even a jaguar? While looking for cats along a treelined trail, we noticed ethereal lights gliding through the dense canopy of the rainforest. These were not the more or less stationary flashes of our local fireflies engaged in the mating game. Oh no, these bioluminescent creatures had lights full on and were clearly going somewhere in a hurry. When asked about the identity of these spectral fliers, our guide declared them to be headlight beetles.  What? I’ve seen lots of beetles and other bugs stuck to headlights of cars, but headlight beetles, really?

Strange creatures can be seen on a nighttime adventure through the tropical rainforest of Belize. As we walked along a trail looking for jaguars, we were confronted by a pair of tiny headlights coming at us on the forest floor. The headlights belong to click beetle known as the headlight beetle or fire beetle. Bioluminescent organs on its thorax produce an ethereal greenish light thought to be the most brilliant in the insect world. Headlight beetles are kin to fireflies like the ones we met in previous videos. A remarkable chemical reaction in specialized cells called photocytes produces light with virtually no heat. How cool is that?

Our search for large cats continued and although we never spotted a jaguar or an ocelot, Lady Luck smiled on us when a tiny pair of greenish headlights appeared on the trail and were headed our way.  Head lamps and cell phone lights revealed a startling click beetle bearing a pair of phosphorescent “headlights” on the trailing edge of its prothorax, the first thoracic segment just behind the head. Bioluminescence of headlight beetles originates from a chemical reaction also found in its cousin the firefly, a.k.a. lightning bug, we met in previous episodes. The miracle of their eerie greenish-yellow light comes from a remarkable chemical reaction in cells lining specialized light organs found in the beetle’s thorax and abdomen. Cells called photocytes contain a chemical, luciferin, a compound that can absorb and store energy from UV light. Luciferin breaks down in the presence of oxygen with the help of an enzyme called luciferase. The breakdown product, dioxetane, is unstable and decomposes into carbon dioxide and ketones. This decomposition releases energy that is emitted as a burst of light. How cool is that! Unlike incandescent light bulbs in our homes, this process is so efficient that almost no heat accompanies the light. Flashes of lightning bugs and headlight beetles are termed cold light. The larvae of the headlight beetle, like glow-worms, the larvae of its firefly cousins here in the DMV,  also produce light.  

Atop the great pyramid at the Mayan site of Xunantunich mysterious forces from the past make visitors do strange things.

The eerie light we witnessed gliding through the rainforest canopy was actually light emitted from the light organ on the abdomen of the headlight beetle. These organs are exposed when the beetle opens its wings and takes flight. One species of fire beetle, Pyrophorus noctilucus, is locally known as the Cucujo. Its bioluminescent light is purported to be the brightest of its kind in the world. Historical accounts claim that indigenous people in the tropics would tie Cucujos to their big toes to help light their path on nocturnal journeys. Another story has it that “a dozen of these beetles placed in a perforated gourd sufficed as a reading lamp.” Now that’s one enlightening tale.

Acknowledgements

We thank Drs. Dan Gruner and Paula Shrewsbury, the hearty crew of BSCI 339M: Tropical Biology and Maya Culture, and our fearless guides Mark and Wilson at T.R.E.E.S. for providing the inspiration for this episode. Fascinating articles including “A new orange emitting luciferase from the Southern-Amazon Pyrophorus angustus (Coleoptera: Elateridae) click-beetle: structure and bioluminescence color relationship, evolutional and ecological considerations” by Danilo T Amaral, Gabriela Oliveira, Jaqueline R Silva, and Vadim R Viviani, “Latin American Insects and Entomology” by Charles L. Hogue, and “Bioluminescent beasties” by Kit Chapman were consulted to prepare this episode.  

A friendly encounter with a very large tarantula: Red Rump Tarantula, Tliltocatl vagans

 

Beautiful red rump tarantulas are powerful nocturnal hunters of small creatures in the rainforests of Belize.

 

As chilly weather continues to plague much of the country including the DMV, we continue our adventures in the Belizean rainforests with eighteen adventurous students from the University of Maryland eager to explore the mysteries of Mayan culture and learn about fascinating creatures and plants in tropical ecosystems. In recent weeks we visited busy stingless bees pollinating bananas and fearsome assassin bugs patrolling vegetation in search of prey. This week, let’s get up close and personal with some nocturnal rulers of the epigeal realm.

While prowling around a landscape near Clarissa Falls, Belize we happened upon a golf ball sized hole in the ground. Using a time-honored trick to “fish” for tarantulas, we inserted a slender twig into the burrow. A large and beautiful red-rump tarantula emerged from her den to investigate the intrusion. Her glorious appearance provided students with an opportunity to see this magnificent rainforest predator up close.  She obliged us with a short capture showing no inclination for aggression whatsoever and glammed for the cameras as we examined her impressive powerful fangs. After a brief photo shoot, we returned her to her lair. While holding a large spider seems a bit extreme, we have visited red-rump tarantulas on previous trips to the rainforest and some bold students have had the opportunity to hold these marvelous hunters.

Using a time-honored trick of tarantula wranglers, we were able to coax a gorgeous red rump tarantula from her subterranean home by teasing her with a small twig. Once she emerged from her gallery, it took a minute or so to corral her and gently pick her up. Students were interested to see her magnificent fangs and this gentle giant seemed happy to oblige. After glamming for the students and posing for pictures, we thanked the tarantula, bid her adieu, and returned her to her gallery.

Much lore and misinformation surround these fascinating predators. Tarantulas are named after Taranto, a city in southeastern Italy on the Ionian Sea. In the 15th through 17th centuries, legends told of the fearsome bite of the Italian tarantula that caused a condition known as tarantism. Tarantism was manifested by heightened excitability, restlessness, and sometimes an irresistible urge to dash about. Legend had it that the disease could only be cured by listening to lively frenetic music, called the Tarantella, or by engaging in a frenzied whirling dance that could last several days - shades of Saturday Night Fever. The culprit behind this mischief was actually a wolf spider, Lycosa tarantula, locally known as a tarantula. Wolf spiders belong to a family known as Lycosidae. True tarantulas such as the ones we encountered in Belize belong to a family of large hairy spiders know as Theraphosidae. These unusually large spiders sometimes measure almost a foot from tip to tip of their extended legs. They have remarkable longevity and can live in excess of thirty years. Their bite is memorable by virtue of some very large fangs hidden beneath the head of the spider. Fortunately, the bite of the red rump tarantula is not very venomous and usually results in a bit of localized swelling, pain, and itching rather than a wretched death.

This beautiful tarantula seemed as curious about humans as humans were about it.

Tarantulas have one of the most interesting mating rituals of any animal in the rainforest. The male tarantula is much smaller than his mate and to successfully sire a brood of young, he places his life at risk in the presence of a potentially hungry female. To complete his task, the male tarantula constructs a thin web on which he deposits sperm. Small leg-like appendages called pedipalps located near his jaws are used to pick up the sperm and carry it about. When he encounters a potential mate, he busts his best move which may include drumming, waggling of legs, and other gambols. This dance helps his mate recognize her suitor as a member of the same species. We all know how disagreeable it is to misidentify members of another species when we are searching for a mate. With the preliminary introductions out of the way, the male warily approaches the female and does his best not to get eaten. The male tarantula is equipped with special claws on his front legs that help him grasp the female while he uses his pedipalps to carefully place sperm into a pouch on her underside. Sometimes the male escapes this romantic encounter, but sometimes he does not and becomes dinner instead. 

On the steps of El Castello at the Mayan ruin of Xunantunich, students discover Mayan history and culture in a tropical rainforest where amazing insects and spiders abound.

The female tarantula lays several hundred eggs in a silken ball. These eggs are stored in the burrow and tended until they hatch. These large juicy arthropods would seem like a tempting meal for other predators in the jungle. However, in addition to sharp fangs, the tarantula has another potent defense. The abdomen of our tarantula was covered with a dense coat of hairs known as urticating hairs. When the human encounter became just a little too unsettling, the spider raised its abdomen and expelled hairs by rubbing them off with the hind legs. These irritating hairs can lodge in the eyes or nasal passages of a would-be predator and thereby thwart an attack. On several visits to the Belizean rainforest, we have encountered tarantulas, enjoyed their company, and returned them to their galleries. However, due to habitat destruction and collecting for the pet- trade industry, tarantulas in the genus Tliltocatl are threatened and are now protected by the Convention on International Trade in Endangered Species of Wild Fauna and Flora laws. These regulations prohibit the international trade of more than 34,000 species of wild animals and plants to prevent their extinction.

Reference

We thank Drs. Dan Gruner and Paula Shrewsbury and the hearty crew of BSCI 339M: Tropical Biology and Maya Culture for providing the inspiration for this episode of Bug of the Week. Special thanks to Mary Lanahan, Rayleigh Graves, and Paula Shrewsbury for providing images and videos used in this episode. Much of the information for this Bug of the Week came from Jerry G. Well's delightful book "The Guide to Owning a Tarantula".

A pair of pretty assassins: Assassin bugs, Reduviidae, in the rainforest

 

Don’t let the brilliant color of this gorgeous Saica assassin bug fool you. The hook at the tip of its beak spells trouble for small creatures on the rainforest floor.

 

Among the spoils of a decimated colony of some unidentified sucking insects, this handsome assassin bug poses for a bug geek.

Last week we traveled to the rainforests of Belize to meet beguiling stingless bees. This week we continue our adventure in the rainforests of Belize where we meet two members of the assassin bug clan. In some of the most-watched previous episodes, we saw a ferocious assassin bug called the wheel bug dispatching stink bugs and impaling caterpillars with its terrifying proboscis. While strolling through an orchard at the Toucan Ridge Ecology and Education Society we came upon a magnificent plantation of Inga trees. These beautiful trees, native to the American tropics, are favorites among foresters and coffee plantation owners by virtue of their rapid growth, delicious edible fruit, and ability to improve poor soils with magical nitrogen-fixing properties. In addition, some species have extrafloral nectaries, small glands that produce sugar-rich nectar to attract beneficial insects. Not only do these nectaries deliver an element of protection to Inga but they also provide a modicum of pest control to crops like coffee trees growing nearby. Despite their admirable growth characteristics and ecosystem services, Inga trees are not immune to their own pest problems. On several of the Inga trees patches of flocculant white wax coated the undersurfaces of leaves. Coatings of white wax are a telltale sign of sucking insect pests like scales, whiteflies, aphids, and mealybugs. We found oodles of white wax, but search as we might all the wax-producing insects had vanished. Roaming around the leaves were several pretty pale green, long-legged bugs with rows of black spots along their backs and patches of yellow-orange adorning heads, legs, and derriere. We could not pin down the identity of this beauty, but it had a strong resemblance to assassin bugs in the genus Zelus we met in a previous episode.

See the dense forest of tiny hairs on the forelegs of this assassin bug. Like biological Velcro they help the bug snare its prey. And look at that terrifying hooked beak, perfectly designed for impaling its victims. We found this gorgeous predator wandering the rainforest floor perhaps in search of a tasty invertebrate for lunch. On the leaves of a nearby Inga tree, other pretty assassin bugs rested amidst the waxy remains of a disseminated colony of sucking insects. As we tried to record this predator, it did its best to escape the nosy lens of the camera. 

At the Mayan ruin of Xunantunich, students discover Mayan history, culture, and insects of the tropical rainforest.

Nearby, at the edge of the Inga orchard, a brilliant red assassin bug in the genus Saica prowled the leaves and grasses on the ground looking for something to stab with its extraordinary beak. Little is known about the feeding habits of these slender legged assassin bugs. Some of their relatives prey on spiders and other ground dwelling invertebrates. These assassins amble about on middle and hind legs thereby freeing up their front legs to capture prey. Their modified prey-capturing legs are called raptorial legs. The upper segments of the assassin bug’s forelegs were festooned with hundreds of small prickly hairs designed to help grasp hapless victims destined to fill the belly of the beast. But as I had a closer look at this tiny terror, I marveled at its beak, the business end of the assassin bug. Unlike other assassin bugs I know that have powerful but unremarkable beaks, this one had a baleful hook at the tip of its proboscis. All the better to impale and subdue its prey I suppose. So many tiny wonders are to be found in the tropical rainforests of Belize.        

Acknowledgements

We thank Drs. Dan Gruner and Paula Shrewsbury and the hearty crew of BSCI 339M: Tropical Biology and Maya Culture for providing the inspiration for this episode of Bug of the Week. The fascinating references “Saica Amyot & Serville, 1843 (Reduviidae, Emesinae, Saicini): taxonomic revision and phylogenetic analysis with morphological characters” by Valentina Castro-Huertas and Maria Cecilia Melo, “Extrafloral nectaries of associated trees can enhance natural pest control” by M.Q. Rezende, M. Venzon, A.L. Perez, I.M. Cardoso, and Arne Janssen, and “Evolution of the assassin’s arms: insights from a phylogeny of combined transcriptomic and ribosomal DNA data (Heteroptera: Reduvioidea)” by Junxia Zhang, Eric R. L. Gordon, Michael Forthman, Wei Song Hwang, Kim Walden, Daniel R. Swanson, Kevin P. Johnson, Rudolf Meier & Christiane Weirauch, were consulted to prepare this episode.

Bananas in Belize get some help from stingless bees: Stingless bees, tribe Meliponini

 

Stingless bees in the genus Trigona are important native pollinators for their evolutionary plant partners in Belize, and also for non-native crops like bananas.

 

In the last episode, we visited non-migratory monarch butterflies enjoying benign temperatures in Florida while many of us shivered under bone chilling weather in other parts of the country. This week we head further south to Belize to visit amazing stingless bees in the tropical rainforests of Belize. Let’s go!

While several workers guard the entry to the colony, a pretty worker is on its final approach to the nest.

While visiting the Toucan Research Ecology and Education Society, we stumbled on a young banana tree in its blooming glory. There, amongst the blossoms, a bevy of stingless bees were busily pollinating a remarkable blossom. For many, the notion of stingless bees is an alien concept. I once had a viewer comment that these could not be bees because they did not sting. Well, a large clan of bees belonging to the tribe Meliponini are true bees with a wide distribution around the world. They live in colonies and make honey. Although they do not sting, they have other defenses which we will visit below. Typical nesting sites for stingless bees include tree hollows and crevices in the ground. Often these hollows have rather large openings. To limit access to the colony and facilitate defense, these large openings are narrowed to trumpet-shaped entrances constructed with a sticky substance called propolis, a mixture of wax and other materials. This creates a defensible portico where ants and other nest raiders, those that would love to enter the colony and plunder the honey, pollen, and baby bees inside, can be repelled.

In addition to natural cavities, stingless bees take advantage of human-made structures to build their nests. While visiting Mayan ruins at Xunatunich and the Jaguar Preserve in the Cockscomb Basin Wildlife Sanctuary, we discovered several colonies of stingless bees occupying cinder block walls of a building where small cracks in the mortar provided perfect entryways to the hollow cavities inside the walls. One colony in a cinder block wall was comprised of stunningly beautiful delicate bees in the genus Tetragonisca known locally as mariolas. They went about their business seemingly oblivious to students and a bug geek with a camera. However, a second darkly colored species of Trigona was not nearly as docile. The nest entrance was guarded by several workers that watched carefully and mounted a surprising attack when humans ventured too close. The assault consisted of dozens of workers flying into faces and hair of the nearby humans. They seemed to pay special attention to eyes, noses, and ears. Although they lacked stingers, their annoying bites were very persistent, forcing the intruders to vacate the vicinity of the hive. In his book “The Insect Societies”, E.O. Wilson describes accounts of stingless bees attacking human intruders. Some species eject an irritating liquid that causes a burning sensation to skin. This trick has earned them the local name of cagafogos, or “fire defecators”, in Brazil. So potent is this defense that it may dissuade very aggressive attackers like army ants from entering nests.

Bananas are one of my favorite fruits. And in the rainforests of Belize native stingless bees pollinate this non-native plant in addition to myriad native plants with which they evolved. Worker bees gather sweet nectar and rich pollen and return it to the hive to feed the queen and bee babies. When their work is complete and pollination is accomplished, the banana says goodbye to the blossoms and the bees.

A visit inside a stingless bee colony would reveal the queen busily filling brood cells with eggs, most of which will become workers. The life of a worker bee is a predestined regimen of tasks that change as the bee ages. For the first several days of life, worker bees are craftsman shaping and forming the basic building materials of the colony, wax and a wax-like material called cerumen. After a week or so and for several weeks thereafter, workers stock cells with food and have the heady assignment of feeding the queen. About this time, they also begin to produce wax to build the many structures of the nest. Soon workers enter guard duty at the nest entrance. Shortly thereafter, they take on the assignment of collecting nectar and pollen for the hive.

Typical nesting sites for stingless bees include tree hollows and crevices in the ground. In addition to natural cavities, stingless bees take advantage of human-made structures to build their nests. While visiting Mayan ruins we saw a colony of Trigona bees nesting in a crack in a palace wall. At the Jaguar Preserve in the Cockscomb Basin Wildlife Sanctuary, we discovered several colonies of stingless bees occupying cinder block walls of a building where small cracks in the mortar provided perfect entryways to the hollow cavities inside the walls. To limit access to the colony and facilitate defense, trumpet-shaped entrances constructed with a sticky substance called propolis create a defensible portico to repel ants and other nest raiders.

At the Mayan ruin of Xunantunich, students discover Mayan history, culture, and insects of the tropical rainforest.

Worker bees are common visitors to many kinds of flowering plants in the Belize and many other Central American rainforests. I have captured some species and gently rolled them between two fingers. Don’t ask why I did this, but they emitted a pleasant floral odor before I released them. For centuries, ancient Mayans maintained colonies of stingless bees to produce honey used for sweetening foods and to produce a fermented drink similar to mead. Unfortunately, with the introduction of Africanized bees and domestic honeybees, the number of colonies of stingless bees has declined dramatically and husbandry of stingless bees is becoming a lost art. In addition, fragmentation and loss of natural forests in Central and South America threaten many species of marvelous stingless bees and the tropical plants they evolved to pollinate.

Acknowledgements and References

We thank Drs. Dan Gruner and Paula Shrewsbury, the hearty crew of BSCI 339M: Tropical Biology and Maya Culture, and our fearless guide, Wilford, for providing the inspiration for this episode of Bug of the Week.  The fascinating book "The Insect Societies" by E.O. Wilson, and the articles “Behavioural and developmental responses of a stingless bee (Scaptotrigona depilis ) to nest overheating” by Ayrton Vollet-Neto, Cristiano Menezes, and Vera Lucia Imperatriz-Fonseca, and “Maya Beekeeping Tradition Fades” by Stefan Lovgren were used as references for this Bug of the Week.