Thursday, 10 July 2008

A Closer Look at the Caterpillar

After my Fungivorous Caterpillar post yesterday, Tim Eisele asked a very good question as to whether I had seen prolegs. The lack of prolegs may have suggested a beetle larva. My initial ID yesterday was based only on the shape of the head capsule and the large amount of silk webbing. There are some Coleoptera with silk glands although I'm not aware of any which make such a large amount of webbing over there food source. If anyone is aware of such a beastie please let me know. In any case I needed to get a closer view.

The following shots were taken with my macro lens under better lighting than yesterdays. The first image shows a series of prolegs. There are at least 6 pairs visible plus the anal claspers which makes 7. There may also be another pair just out of view one segment closer to the head. The prolegs are not well developed.

Caterpillars generally have 5 pairs of prolegs although some have less and some, such as those of the family Micropterigidae, can have 8 pairs of prolegs. The presence of prolegs does not in itself prove that the larva is Lepidopteran. The larvae of some other orders can also have prolegs. The one sure way to identify it as a caterpillar is to look for crochets - hook-like spines that form a ring around the prolegs. For this I dragged out my el cheapo microscope. The problem with the microscope is that it lacks depth of field. I really need to get myself a proper binocular, disecting microscope. I did eventually manage to focus on a single proleg and found it did indeed have crochets. So I can now say for sure that this is a caterpillar. I would love to have photographed this but the microscope camera did not come with a driver for Linux.

I could not find any true legs. There are some caterpillars which have reduced or absent true legs. The second photo does show what may be one leg making an appearance. You can be the judge of that.


Not the best photo but you can make out the reduced prolegs


Is that a "true leg" sticking out from below the thorax?



5 comments:

  1. Goodness! I'm not one to ask about "true legs", mine are bundled up in a blanket while I hop around in the cold. Fascinating read though!

    ReplyDelete
  2. Blanket! Why didn't I think of that? Goes of to get blanket and beanie......

    ReplyDelete
  3. Hi there,

    It is probably a fly larva (maggot if you must). There are several families that retain sclerotised head capsules that also feed on fungi (Mycetophilidae, Sciaridae).
    eg.http://bugguide.net/node/view/265748

    ReplyDelete
  4. Hi there,

    It is probably a fly larva (maggot if you must). There are several families that retain sclerotised head capsules that also feed on fungi (Mycetophilidae, Sciaridae).
    eg.http://bugguide.net/node/view/265748

    ReplyDelete
  5. Thanks Dave - Fascinating. I wasn't aware of that.

    P.S. Sorry I missed your comment, hence the late reply.

    ReplyDelete