Discoveries, Entomology

A [Local] Monster Mash

By Shelby Perry –

Here in Vermont you can hardly go outside without seeing signs about buying local.  Local foods are labeled in grocery stores, restaurants proudly display maps of Vermont with pins pointing out where they source their ingredients, and everybody who’s anybody seems to have a CSA share. But for some reason every year around this time even the most devout locavores import their Halloween monsters from far away.  Mummies more at home in Egypt smile out at you from windows, tarantulas usually found in tropical regions crawl all the way into candy bowls in Vermont, and vampires hop planes from Transylvania to lurk on residential porches for a few weeks every October.  Enough!  I say it’s time to put an end to the madness of imported creepies and crawlies, and to get to know a few of our own.  And so, I present to you a Halloween line-up of locally and sustainably sourced (and not-so-scary) monsters:

The Stigmata Mummy-Wasp (Aleiodes stigmator)

Mummified Acronicta Caterpillar with exit-holes of Stigmata Mummy-Wasp, photo by Bryan Pfeiffer
Mummified Acronicta Caterpillar with exit-holes of Stigmata Mummy-Wasp (Photo by Bryan Pfeiffer)

Here’s the good news: the stigmata mummy-wasp didn’t make the monster list for having a painful sting. In fact, these wasps are small and don’t have stingers.  In place of a stinger on their hind end, these wasps sport an ovipositor, which they use to inject their eggs under the skin of an innocent and unsuspecting host caterpillar.  After the eggs hatch the wasp larvae chew a hole in the underside of the caterpillar, causing it to leak fluids that dry and essentially glue the caterpillar to a plant.  Next the larvae mummify the caterpillar by eating the soft innards and lining the empty body with silk.  Inside the hollow caterpillar husk the wasp larvae spin their own cocoons and pupate into adults.  When they emerge from their cocoons they chew their way out, leaving behind the dry husk of a caterpillar that looks like it has been sprayed with buckshot.

Even though this may sound straight out of science fiction, stigmata mummy-wasps are native to Vermont where they generally inhabit wetlands and floodplains.  Though the wasps themselves are small and hard to find, the mummified caterpillars are not.  Their riddled mummies can be found clinging to sticks year round, and if you find one in late fall you might want to watch it closely – you might be lucky enough to spot one of these little monsters emerging.

The Oleander Aphid (Aphis nerii)

Oleander Aphids on a stalk of Swamp Milkweed
Oleander Aphids on a stalk of Swamp Milkweed

There are many types of aphids, but while I was researching for this list one variety stood out: Oleander aphids.  These little orange and black bugs grab onto a stalk of milkweed (or any of several other plant hosts) with specialized sucking mouthparts and drink it dry.  Their story only gets weirder from there.  Oleander aphids develop from unfertilized embryos and all adults are female; males do not occur in nature.  Adult females can be winged or wingless, the former usually showing up when the host plant is overcrowded or dying so that they can fly off to infest a new host.  Both the winged and wingless adults excrete live nymphs instead of eggs, and a colony can grow quickly.  The nymphs develop through five different phases before becoming adults, but nearly all phases look the same and vary only in size.

If an army of jack-o-lantern colored female clones sucking the life out of a plant isn’t Halloween enough for you, I should also point out that oleander aphids have their own mummifying parasitoid wasp.  The aphidiid wasp (Lysiphlebus testaceipes) lays a single egg inside an aphid nymph or adult.  When the egg hatches the wasp larva consumes the aphid from the inside, so that it develops into a brown papery husk of its former self.  Much like stigmata mummy-wasp larvae, the wasp larva then spins a cocoon inside this mummified aphid, pupates, and chews its way out, leaving behind a bloated brown aphid mummy with a hole in it.  When a dense colony of oleander aphids is heavily parasitized, half or more of the aphids in the colony may eventually be only mummified remains while their sisters slurp placidly beside them.  How bewitching.

Horsehair Worms (Paragordius varius)

Resembling an animated, wiry strand of hair, horsehair worms are often spotted writhing in the bottom of woodland streams and pools. As charming as that may sound, their mating behavior is less than romantic.   When a female indicates a willingness to mate, the male releases a cloud of sperm in her general vicinity, and then swiftly dies.  The sperm forms a glob, which finds its way to the appropriate receptacle on the female within the next 24 hours.  A fertilized female goes on  to lay as many as 6 million eggs, and then she too perishes.  As It turns out this is the least offensive part of their life cycle.

Horsehair Worm (on top of leaf) found in a stream in Bristol, VT

The eggs mature, and in 2-3 weeks millions of tiny worm larvae are hunting for hosts in the pool or brook.  They infect many different kinds of aquatic phase insects, including mosquito larvae, and when the infected larva matures into its adult phase, the worm larva comes along for the ride.  Eventually this intermediate host insect is consumed by the host the worm is really looking for: crickets and their relatives.  Once inside this final host the worm begins to absorb nutrients through its skin from the host’s body.  Having no mouth or digestive system of its own, the worm requires an environment where food comes pre-digested.

While growing inside its host, a process that takes 2-3 months, the worm is also practicing mind-control.  An infected cricket will not chirp at all as chirping uses up precious energy and can attract unwanted attention to the worm’s comfortable home. Once the horsehair worm has fully developed inside of its cricket host (reaching lengths of four inches or more), it releases a chemical that drives the host to seek out water.  Meanwhile the worm has carved a hole in its host’s side, and shortly after the host hits the water the worm will emerge in its free swimming adult phase to mate, leaving its injured but still living host behind to begin the cycle again.

From the mummified remains of caterpillars, to the mind games of a parasitic worm, our Vermont backyards boast a roster of Halloween monsters rivaling those of the silver screen.  So this Halloween, when you find yourself telling scary stories with friends, borrow a tale right from your own backyard…and sustainably source your monsters.

Shelby Perry is a second year student in the Field Naturalist Program.  She would like to acknowledge Field Naturalist Graduate, Charley Eiseman, for his help fact-checking sections of this post, and his wonderful book Tracks and Sign of Insects and other Invertebrates: A Guide to North American Species.  

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