Friday, May 1, 2009
Phantom Midge Larva
Name: The Phantom Midge is a fly in the genus Chaoborus. Its larvae are aquatic with transparent bodies and hence the name Phantom. You might expect something with a name like that to hatch into a no-see-um but that is not the case. The Phantom Midge, from the human perspective, is a friend – it doesn’t bite and the larvae eat Mosquito larvae. No-see-ums belong to a closely related group of insects which like another famous and related group, the Mosquitoes, are blood suckers.
When and where found: Phantom Midge larvae were scooped up along with lots of other little pond critters during the vernal pool walk on April 26. This particular vernal pool is on the Carlisle Conservation Foundation land on the west side of town, off the east side of West Street, just a bit north of South Street. Like a typical vernal pool, this one contained masses of wood frog eggs and spotted salamander eggs. The wood frog egg masses were already breaking up and hatching into tadpoles; the salamander eggs were still embryos. Phantom Midges are common and sometimes the larvae are present in huge numbers. I imagine that most of our vernal pools have the larvae.
Distinguishing characteristics: Phantom Midge larvae are just under an inch long and have a long narrow body with no legs. If they stay still they are not so easy to see but they give away their presence when they move. The most obvious characteristic is the two pairs of dark oval or kidney-shaped sacs, one pair near the head and another near the tail, and the two dark eyes. The dark sacs are air chambers which allow the larvae to just hang out in the water without rising or sinking. Because they are transparent you can see the gut running down the center of the animal. A closer look would tell you what is in it. This is one of those characteristics that I’m glad had no evolutionary advantage for mammals, least of all humans. I’d rather ask friends “have you eaten?” than simply know the answer. The adult Phantom Midge is a long-legged fly and looks a little like a mosquito but when it lands it is likely to rest with its front legs in the air. The mosquito is more likely to have its rear legs in the air.
The ways of predators: Phantom Midge larvae are predators but they have no legs with which to grab their prey. Instead they use long hairy modified antennae which are adapted for grasping. As Stephen Marshall says, “Given that antennae are usually the primary sense organ in insects, an insect that grasps prey with its antennae seems as strange as a vertebrate that grasps prey with its eye.” (I have seen people though at a dessert buffet who come very close to this.) The larvae eat all sorts of small crustaceans and insects and are themselves food for salamander larvae and other predators. Midge larvae of all kinds, not just the Phantoms, are abundant and an important part of aquatic food chains. They use other bodies of water and are not dependent on the pool being ‘vernal’ or free of fish.
Sources: Living Invertebrates, Pearse and Buchbaum; Borror and Delong’s Introduction to the Study of Insects, Charles A. Triplehorn and Norman F. Johnson; A Field Guide to the Animals of Vernal Pools, Leo P. Kenney and Matthew R. Burne.
Submissions: Please feel free to claim this space and write the Biodiversity Corner on any species that has attracted your attention, that occurs in the wild, and was found in Carlisle.
© 2009 The Carlisle Mosquito