Egg Patterns

There is no better designer than nature.

~Alexander McQueen

While out in the yard looking at the tent caterpillars the other day, Melissa turned around and saw an interesting pattern on the trunk of a small tree. The pattern and details of the egg tops told us it was the egg mass of a Wheelbug, Arilus cristatus. Wheelbugs (and many other members of this family of insects known as assassin bugs) typically lay a patch of eggs covered with a resinous substance that hardens as it dries. This is a fairly large egg mass, measuring about 2 inches from top to bottom. If you are bored inside today, perhaps you can guess how many eggs are here, and then count them…you may be surprised.

184 wheebug eggs

Egg mass of a Wheelbug attached to a small tree (click photos to enlarge)

A closer view shows the typical fringe-like border around each egg top. I’m not sure what the function is, but I am guessing it could be to increase surface area for oxygen absorption.

184 wheebug eggs closeup

Close-up of the egg mass shows the fringe along the top of each egg.

A side view shows the eggs are somewhat bottle-shaped and tightly stacked together. One reference described the eggs as looking like “brown bottles with fancy stoppers”.

wheell bug eggs from side

Side view of eggs…the tiny dots are pollen grains.

These should hatch sometime later this spring and a horde of tiny reddish-orange and black (at first) robotic insects will be unleashed. I am guessing they may prey on one another as well, so their numbers will be greatly reduced before they reach adulthood in late summer (there is one generation per year). Once they are at that stage (over an inch long), they are formidable predators of many types of insects from caterpillars to bees. They are important predators of some pest species like the introduced and invasive Brown Marmorated Stink Bug, and some hairy caterpillars (like tent caterpillars) that are avoided by many birds. With their distinctive gear-like crest and large size, they are fascinating to observe, but handle them cautiously (or better yet, not at all), as they can inflict a painful bite with that long, needle-like beak.

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An adult Wheelbug with its namesake armament and strong, piercing-sucking mouth part.

By the way, I counted 184 eggs in this group.


The present was an egg laid by the past that had the future inside its shell.

~Zora Neale Hurston

A quick update on the tulip-tree silk moth eggs from my last post – they hatched!

Tulip tree silk moth eggs hatching close up

Close up of eggs hatching – viewed from below in clear plastic container (click photos to enlarge)

The moth laid eggs inside the container on the night of May 19. They started hatching early in the morning on May 30. They hatched as a group and within about 15 minutes, they all had emerged. I placed a leaf of their host plant, tulip poplar, in the container and they all gathered along the edge and started to feed.

tulip tree silk moth caterpillars after hatching

Tulip-tree silk moth larvae feeding as a group

This species feeds as a group in their early stages, then separate out and feed solo as they grow. I have never seen the early instars of this species before, but references say these are often high in the treetops. My plan is to release most on tulip poplar saplings around the Garden and here at home and then raise a few for programs (the above photo represents about half of the group that hatched).

tulip tree silk moth caterpillars after hatching 1

First instar tulip-tree silk moth larvae

They have a lot of eating and growing to do over the next few weeks. Mature caterpillars look very different (pale green with a few bright red and yellow bumps) and are a couple of inches in length. It turns out these were not the only eggs that hatched this week…

Assasin bug egg before hatching 1

Mystery egg in yard

As I always do when walking around the yard, I was scanning the vegetation looking for anything of interest when my eye caught a small egg on top of a leaf. I leaned in and took a closer look and saw some beautiful patterns – I could see the creature inside the egg! The egg was about 2mm long and contained what looked like legs ending in tiny black claws. There were some large dark dots, that I assumed might be developing eyes.

Assasin bug egg before hatching

Back-lighting the egg gave it the look of a miniature alien pod

I brought the leaf inside to photograph. The more I looked, the more it resembled a tiny alien from some sci-fi thriller. Ironically, I had found a similar egg the week prior on a hike at work as part of a citizen science program called Caterpillars Count. I had looked that one up in my go-to resource for such things, the excellent Tracks and Signs of Insects and Other Invertebrates by C. Eiseman and N. Charney. Both eggs closely resembled their photo of the egg of leaf-footed bugs. I decided to wait and see what hatched. I didn’t have to wait long. The next day, I took it to work to show a few folks, and while I was in a meeting (dang meetings!), it hatched.

Assasin bug hatchling

Newly hatched mystery bug

It resembles assassin bug nymphs I have seen in the past, so that is what I first called it. But, I looked up leaf-footed bugs in my other go-to resource, Bug Guide, and there were photos of my same egg and nymph. So, this little guy is in the genus Acanthocephala, and will grow into a large (30mm long) true bug that feeds on plant juices, fruit, and other plant parts. It has a lot of growing to do before it will look like its picture in a field guide.

Assasin bug egg after hatching

Empty egg shell of leaf-footed bug

Once again, the world outside my door has proven to be fascinating and full of mystery and beauty. Guess I will be looking for more eggs in the coming weeks to see what emerges.