Pits of despair for ground dwelling insects: Antlions, Family Myrmeleontidae

 

This gorgeous adult Glenurus antlion made a surprising guest appearance on a window screen. Image credit: Ken Paynter

 

Conical pits in dry soil spell danger for ants and other small ground-dwelling arthropods. Death awaits at the bottom of the antlion’s pit.

Some of you may recall a memorable desert scene from George Lucas’s Return of the Jedi were a terrifying multi-toothed creature called a Sarlacc inhabited a pit on Tatooine and dined on hapless Jedi Knights. Each year miniature versions of Sarlaccian pits appear in the dusty desert beneath the overhang of my tractor shed. These craters, ranging in diameter from the size of dimes to larger than quarters, mark the killing field of antlions, the larval stage of nerve-winged insects (Neuroptera) known as Myrmeleontidae. One of my curious pastimes is to watch ants, beetles, and other small ground dwelling arthropods stumble into the craters and tumble down the slope. At the base of this cone of death lies the ferocious predatory antlion.

Wicked jaws of the antlion larva capture victims and drain their blood. Jaws are also used to construct the antlion’s pit and flick sand to capture prey.

The antlion larva, affectionately known as a doodlebug, constructs its funnel-shaped trap by backing into sandy soil and carefully flicking soil particles with its mouthparts until a symmetrical pit forms. Small ground-dwelling arthropods like ants fall into the pit and tumble to the bottom. At the base of the pit just beneath the sand, the antlion awaits its prey. Sensing that someone has dropped in for dinner, the antlion flicks sand particles upward until the victim tumbles to the bottom of the pit where the ill-fated quarry meets a lethal embrace with powerful jaws of the antlion. The victim is often dragged entirely beneath the sand as the antlion enjoys its feast. Jaws of the antlion bear a groove used to channel blood from the living victim to the belly of the beast. After consuming the liquid portion of the prey, the antlion tosses the carcass from the pit with a snap of its head. Occasionally a large or lucky potential victim will evade the first strike and attempt a desperate scramble for freedom up the slope. To foil the escape, the antlion again flicks sand from the base of the cone towards its prey. The displacement of sand creates a Lilliputian avalanche carrying the prey down slope into the grasp of the antlion.

In the dry soil beneath the overhang of a shed, small pits in the soil mark the kill zone of antlions. Watch as an antlion larva disappears beneath the earth. Once buried it constructs a conical pit to trap its prey. Among the carcasses of a beetle and a daddy-long-legs, a hapless ant attempts a desperate scramble out of the antlion’s pit, all to no avail. Soon the ant will be pulled underground and drained of its blood. The ant’s carcass will be added to those of other victims near this pit of despair. The beautiful adult stage of an antlion is often mistaken for a dragonfly or other winged insect.

Adult antlions sometimes frequent vegetation in my garden. Females will find mates and return to dry sandy soils around my home to lay eggs in the soil.

Adult antlions are rarely seen, but are often mistaken for a damselfly or dragonfly. Feeding habits of these beautiful creatures are largely unknown other than that they consume soft-bodied insects and pollen. They are often attracted to outdoor lights at night. These delicate insects lay eggs in sandy soil where eggs hatch into subterranean monsters. Upon completing development, antlions spin silken cocoons in the soil where the transformations from larva to pupa to adult takes place. So, while hiking in the desert, if you come across a deep conical pit, stay well back from the edge lest you tumble in. You never really know what waits at the bottom.

Acknowledgements

References for this Bug of the Week include “Effects of slope and particle size on ant locomotion: Implications for choice of substrate by antlions” by Jason Botz, Catherine Louden, Bradley Barger, Jeffrey Olafsen, and Don Steeples, and “Immature Insects” by Frederick Stehr. The inspiration for this Bug of the Week came from Ken Paynter who shared the wonderful image of Glenurus with us.

Mellow mallow bees, Ptilothrix bombiformis

 

This pretty Ptilothrix bombiformis took a time-out from the business of gathering food for her young to glam for the bug geek with a camera.

 

In 1966 during the construction of the planned city of Columbia, MD, a 27-acre reservoir named Lake Kittamaqundi was created from several unnamed tributaries of the Little Patuxent River. In the intervening decades, along the banks of Kittamaqundi patches of marshmallow, Althaea officinalis, put down roots and now show off their dazzling floral displays, five large petals dressed in shades of white, lavender, pink, and purple. From June into early autumn, marshmallows and other members of the hibiscus clan are visited by Ptilothrix bombiformis, an apid bee that specializes on members of the mallow clan. An encounter with this charming bee began on a sunny morning while walking along a trail that circumnavigates the lake. My eagle-eyed companion noticed several small bees darting in and out of turreted pencil-sized holes in the hard clay soil on the bank of the lake. These cute bees, Ptilothrix bombiformis, are unique in that they are one of only two species in the genus Ptilothrix found in the US.  Ptilothrix bombiformis occurs mostly in the eastern half of the US and its sister species occurs in Arizona and New Mexico.

A Ptilothrix bee begins to build her nest by wetting hard mud and digging with jaws and legs. Off she goes to get more water for softening the soil. She regurgitates water to moisten the soil and work it into a turret for her nest. Beneath the earth, water is mixed with soil and mud pellets are removed to enlarge the gallery. Then off she goes to visit mallow blossoms for nectar and pollen. She returns to her nest with provisions to sustain her brood as they grow and develop underground.

Piles of irregularly shaped mud pellets surrounding a turreted hole in the ground mark the nest site of Ptilothrix bombiformis.

These industrious bees construct nests in soil. To excavate galleries in hard-packed earth, females land on the surface of the lake, imbibe water, fly back to the nest site, and regurgitate the water to moisten and loosen the soil. During nest construction the area around each gallery is littered with an array of small mud pellets deposited by the bee as she removes soil to construct the subterranean nursery for her young. Watching these clever bees roll mud balls with their hind legs out of the gallery is highly entertaining. In a nearby patch of marshmallows, mothers gather nectar and pollen to provision their nest with pollen cakes for their young. After providing sufficient food for their brood, the female bee seals the gallery with a plug of mud to prevent parasites and predators from entering the nursery and devouring her youngsters. Ptilothrix bombiformis has taken advantage of human-made features such as the aforementioned shores of Lake Kittamaqundi and roadways passing through marshlands as favorable habitats to construct their nests. Ornamental members of the mallow clan, including Rose-of-Sharon found in residential landscapes are used as sources of nectar and pollen. These behaviors provide opportunities to meet these bees. With some luck and a little nature-focused attention, you may catch a glimpse of these mellow mallow bees in the blossom of a hibiscus or busily tending their pellet-strewn nest sites along the banks of a lake or trails through a marsh.

Acknowledgements

Once again, we thank Sam Droege for generously taking time to identify Ptilothrix bombiformis and share his wisdom about these beauties. Information about the bees featured this week came from Joseph S. Wilson and Olivia Messinger Carril’s amazing book “The Bees in Your Backyard”, and “The Biology of Ptilothrix bombiformis (Hymenoptera: Anthophoridae)” by Richard W. Rust. Many thanks to Professor Shrewsbury for spotting the nest site of Ptilothrix bombiformis and providing video for this episode.

Throwback Monday: Recyclers in the circle of life - Bess beetles, Odontotaenius disjunctus

 

Look who is recycling a dead tree of heaven branch - a family of bess beetles.

 

Two weeks ago, while moving some decomposing logs, I encountered almost mature larvae of bess beetles. Now this may not seem exciting to you, but I have not witnessed these alive in the wild for more than three decades. So, to share this rather unusual event, we will revisit a popular episode from the days of covid in 2020 with the addition of a new video and one new image. Hope you enjoy the episode.

While clearing some logs in Washington County, MD, I encountered a family of bess beetles. One adult and several almost mature larvae were recycling a decomposing tree of heaven branch. Look at the size of the larval galleries in the wood. Don’t worry, after recording the happy family, the branch was returned and the beetles resumed their ecosystem service of repurposing dead wood. 

These powerful jaws can gnaw through even super-tough wood like oak.

This week we meet one of Mother Nature’s champion recyclers, bess beetles, whose mission it is to repurpose tough wood fibers into cute beetle larvae. During the past week or two while wandering wooded trails, I have enjoyed several encounters with magnificent bess beetles as they scurried about the forest floor. Coincidentally, several images of bess beetles have arrived in my mailbox from other folks curious to learn about these lumbering beauties. Bess beetles are also known as the horned Passalus and as patent leather beetles by virtue of their shiny black color (young adults have deep red/brown coloration that darkens to black) and notable horns. These powerful beetles are important participants in the great circle of life. No, they do not occupy an exalted place at the top of the food chain like Mufasa, the Lion King. They sit near the bottom of the heap along with fungi and bacteria, where they help decompose fibrous wood. Adult bess beetles use strong jaws to gnaw and ingest wood. After being processed in the beetle’s digestive system and deposited back in the wood, the microbe-packed droppings, a.k.a. frass, are consumed by bess beetle larvae. The microbes contained in the leavings of the adult beetles are particularly important for young larvae that require parental microorganisms to help them digest wood. Tough plant tissues such as lignin and cellulose are indigestible to us, but the gut microbiome of the bess beetle and resident microbes found in decaying wood enable bess beetles to capture nutrients as they recycle tough plant polymers.

Bess beetles are among the champion recyclers of the insect world. A remarkable microbiome in their gut enables bess beetles to breakdown tough polymers found in wood and extract nutrients locked up inside. Now is a great time to observe bess beetles as they scramble across the forest floor or recycle wood beneath the bark of fallen trees.

Dilemma for a bess beetle at a picnic, “Do I go for the hamburger bun or find a dead tree to eat?” Image credit: Ashley May

Upon plucking a bess beetle from the forest trail, I was intrigued to hear it squeak. Bess beetles are able to produce sound by rubbing their wings across a rasp-like structure on the upper surface of their back just beneath the hard wing covers. This form of sound production is called stridulation. Many beetles, such as the big Bornean beetles we met on February 19, 2024 in “Picking up good vibrations”, stridulate. The larvae of bess beetles are somewhat unique in that they also stridulate by rubbing together two sections of their legs. Several authors suggest squeaking sounds enable both larvae and adults to communicate with others in the decomposing wood. One account indicates that larvae follow the calls of adults in the colony. Perhaps this is a way for parents to assist their babies in discovering food or maybe it conveys a message akin to “eat your vegetables.” Other scientists believe the calls may frighten would-be predators. To learn the true nature of the call of the bess beetle, I made a recording of the sound. By playing the sound backward at very slow speed, the beetles could clearly be heard trilling the Gershwin classic “summer time and the livin’ is easy.” I guess summer must have arrived.

Acknowledgements

Bug of the Week thanks Ashley May for inspiring this episode and providing the nice image of a bess beetle that apparently joined her picnic. Dr. Shrewsbury helped wrangle bess beetles in the wild. Information for this Bug of the Week came from two fascinating papers “Gut anatomical properties and microbial functional assembly promote lignocellulose deconstruction and colony subsistence of a wood-feeding beetle” by Javier A. Ceja-Navarro, Ulas Karaoz, Markus Bill, Zhao Hao, Richard A. White, Abelardo Arellano, Leila Ramanculova, Timothy R. Filley, Timothy D. Berry, Mark E. Conrad, Meredith Blackwell, Carrie D. Nicora, Young-Mo Kim, Patrick N. Reardon, Mary S. Lipton, Joshua N. Adkins, Jennifer Pett-Ridge, and Eoin L. Brodie, and “Observations on the life history of the horned Passalus” by L.E. Gray.

Early rising bees in the pumpkin patch: Eastern cucurbit bee, Peponapis pruinosa, and two-spotted longhorn bee, Melissodes bimaculatus

 

Good morning, sir! A male eastern cucurbit bee greets the camera while another gathers food in a pumpkin blossom.

 

Each year I try to grow pumpkins in my suburban landscape in Columbia, MD. Each year roving gangs of white-tailed deer invade my landscape and pillage my pumpkins despite my best attempts to shoo them away or assuage their damage by dousing my pumpkins with deer repellent. One morning last week, shortly after sunrise, while mourning the loss of yet another batch of pumpkin leaves, I was fascinated by clusters of solitary bees jockeying for position to gather nectar and pollen from newly opened blossoms of pumpkins. One of the most entertaining was the eastern cucurbit bee, Peponapis pruinosa. The genus name Peponapis literally means “pumpkin bee.” Sometimes as many as four of these rascals with their stripy abdomens tussled for access to nectaries deep inside the blossom. These wonderful bees are specialists, collecting pollen only from members of the squash family. Females construct burrows in soil a foot or more in depth and prepare several brood chambers along the gallery. Each chamber is provisioned with pollen and nectar to feed the developing young. Larvae develop through summer and autumn and emerge next spring when squash, pumpkins, and other cucurbits start to bloom. While females toil to build their subterranean nurseries, when blossoms close in the mid-morning heat, males can sometimes be found resting inside closed blossoms. These native bees evolved to pollinate their cucurbit hosts and can be found from Canada to Mexico.

Early one morning I stopped by my pumpkin patch and caught a glimpse of eastern cucurbit bees mobbing pumpkin blossoms. They were gathering nectar and pollen to feed their young. Nearby, a two-spotted longhorn bee tidied up a bit before moving to another blossom. Look at the size of her pollen loads. Her legs look like saddlebags. Wow!

A female two-spotted longhorn bee shares a blossom with an eastern cucurbit bee at dawn.

Zooming about my pumpkin patch, but not as numerous as Peponapis, was a gorgeous black bee with smokey black wings and two white tufts of hairs on its abdomen. Melissodes bimaculatus goes by the name of two-spotted longhorn bee. Unlike Peponapis, this native solitary bee is more of a generalist. I often see it gathering nectar and pollen from my cone flowers and other members of the aster family in addition to its sorties at my pumpkins. Hind legs of female bees are festooned with stout hairs called scopa which are used to collect pollen. When fully loaded they look like yellow saddle bags. Like Peponapis, female two-spotted longhorn bees tunnel in the soil and provision brood chambers with nectar and pollen to feed their young. Although these are solitary bees, they often form large aggregations of nests in areas with loose soils that they prefer.  

If you grow pumpkins, squash, zucchini, or cucumbers and you live in the eastern US, grab your cup of coffee and head to the cucurbit patch early in the morning to enjoy these entertaining and beautiful native pollinators. 

Acknowledgements

Bug of the Week thanks Sam Droege for generously taking time to identify the heroes of this episode. Information about the bees featured this week came from Tufts Pollinator Initiative, and Joseph S. Wilson and Olivia Messinger Carril’s amazing book “The Bees in Your Backyard”.