Category Archives: Hymenoptera
Zombies are cool, right?
I bought this shirt from EscapePod on Etsy. It’s what all the cool entomologists are wearing these days, featuring an ant infected with the cordyceps fungus.
Basically, the fungus controls the behavior of the infected ant, causing it to climb to an ideal spot and clamp down with its mandibles… and die. Thus allowing the fungus to grow a fruiting body and spread its spores. Infected ants are sometimes called “zombie ants”, not because they rise from the dead, but because of the mind-controlling behavior of the parasite. I’ll let Sir David Attenborough tell you more:
And if you can handle really terrible narration, you can’t miss out on snail zombies:
If you need some fun lunch-time reading, here is an article by Carl Zimmer on “How to control an army of zombies“.
Creepy or cute?
Sawflies, suborder Symphyta, are in the order Hymentoptera alongside bees, wasps, and ants. Their larvae are remarkably caterpillar-like, sometimes confounding entomologists until the larvae are observed up close.
There are some key differences: sawflies have many more prolegs than lepidopteran caterpillars (lep caterpillars have a maximum of 5 pairs, sawflies have 6 pairs or more), and they have only one eyespot on each side of the head (lep caterpillars have 6 stemmata arranged in a half-circle).
For some reason, the eyespots creep me out. I keep thinking that it should make them even more cartoonish and adorable, but I just cannot get on board with loving sawfly larvae. What do you think? Is this guy creepy or cute?
Sawfly larvae can be gregarious, and give themselves away with characteristic resting poses. If you see a bunch of caterpillars along a leaf edge waving their rear ends in the air, you are looking at some sawfly larvae. They also tend to have a slimy looking sheen to them.
Oh, and did I mention some species spit?
They spit. At least this one does, in the family Cimbicidae. Many sawfly larvae simply regurgitate their nastiness, but these have the audacity to express fluid in a stream from glands above their spiracles.
Interestingly, in some parts of the world sawfly larvae are called “spitfires”, even though they do not spit forcibly – instead regurgitating fluid or everting it from glands. Only some species in Cimbicidae can actually hit you in the face from a tree branch a foot away (which the one in the video did, before I started filming).
For more information:
Eisner, T. 1994. Integumental Slime and Wax Secretion: Defensive adaptations of sawfly larvae. Journal of Chemical Ecology, 20:10. Link
Hunting horntails
Another adventure only marginally related to caterpillars. This happened a few days ago.
One of the undergrads in the lab, I’ll call him “The Minister of Silly Walks” (“Silly Walks” for short, he does an impeccable John Cleese impression) went with me to get lunch for ourselves and for the caterpillars. For us, that meant the Subway down the street. For the caterpillars that meant breaking branches off of trees as we walked, trying to not look terribly conspicuous carrying armloads of leaves as we casually walked along the street.
On the way, I noticed some odd insects on the trunk of a dying maple tree. Upon closer inspection, I realized they were horntails! They are in the family Siricidae, in the order Hymenoptera along with the ants, bees, and wasps. This was the first time I had ever seen them in the wild, but their anatomy was unmistakable. Wasp-ish but without a constricted waist, elongated body, and the characteristic “horn” at the end of the abdomen. I at first assumed this was an ovipositor, but as I examined the insects more closely, they were not using them to poke into the tree. Instead, they were wiggling their bodies side to side, not moving from their spots even as we approached with our cameras.
It turns out the ovipositor actually originates much further up on the body, and is the thin black line you see extending from the horntail to the tree in the photo above (seen between the middle and hind leg). We determined this species is most likely Tremex columba, and the individuals we observed were all ovipositing females. They lay eggs into dying trees, and their larvae eat the soft bark. These larvae are often parasitized by Megarhyssa wasps, who use their long ovipositors to lay eggs directly into the larvae. Luckily for the horntails, there were no wasps in sight that day.
Interestingly, some females died during this process, and were stuck into the tree by their ovipositor. Silly Walks decided to retrieve a few of these to bring back to the lab. This was one (successful) attempt.
Ah, what entomologists will do for a prize.
Mega
A couple nights ago it was raining, as usual. I kept my blacklight on, though, since it was just sprinkling on and off. Only a few moths came to the light, along with a smattering of beetles. I was about to give up and go to bed when I saw this lovely lady buzzing around. WOW!!!
She is Megarhyssa atrata, the Giant Ichneumon, and take a look at that ovipositor! Female ichneumonid wasps such as these use that long contraption to bore into wood and reach a soft squishy insect target inside, usually a horntail wasp larva. They will then lay an egg inside the larva’s body, and the young will hatch and eat it from the inside out.
I had never seen one of these alive before, and pinned specimens are usually beat up and broken. I was so impressed (and sleepy) that I decided to let her live (hey, I keep a kill jar by the door for times such as these). However when I opened the screen door to go back in the house, she followed me in! So we played a game of tag around the lights in my living room for about 10 minutes, with her pretending to sting me every time I got my hands on her… until I finally wrangled her safely and threw her outside. She bounced off my blacklighting sheet a few times and fluttered back into the woods. Definitely an interesting encounter.
caterpillarblog 