Tuesday, June 3, 2014

Strange "Cats" In The House

Sawfly larvae - Bob Barker*
Unlike mammals which nurture their young, most insects reproduce on the Walmart theory of high volume, laying hundreds of eggs which produce tens of larvae and hopefully a few adults survive to reproduce.  Judging by the numbers this system works well for most.

In the Butterfly House at Close Gardens, volunteers bring in a number of butterflies to mate, lay eggs and hatch caterpillars to feed on native host plants and complete their life cycle in the relative security of a nursery.  Occasionally a collection of foreign creatures appear, munching on the free food that has been raised for the more charismatic Lepidoptera.  They were not the desired species but still are an opportunity to learn about nature.  An example was this message to Kevin Firth.
"We just got a call from one of the docents...there are black caterpillars all over the willow tree and no one seems to know what they are. Can you please write what they are into the log book? I do know there are tons of webworm moth cats in the house just running around."
Kevin's first response was identifying them as willow sawfly (Nematus ventralis) larvae.   "They will not do any harm (except to the willow), and they give us an opportunity to show people how to distinguish between Lepidopteran larvae (caterpillars) and other similar larvae. The key is the number of pairs of prolegs--Lep larvae will have four or fewer pairs, sawflies will have five or more pairs. The sawflies are stingless wasps and are so named for a saw-like organ that the females use to cut into the foliage/twigs of the host plant to lay their eggs."

They may produce multiple generations in a year while the larvae can overwinter for two or more years before pupating.  They don't cause permanent damage to the willow although they may produce significant competition for the food supply of the butterfly caterpillars in the closed environment of the Butterfly House.

Just like movie stars, charisma in the insect world is highly dependent upon its looks.  These larvae are dramatic in appearance, a dark and sinister black with aposematic bright yellow spots advertising to birds that they don't taste good.  The adult sawfly on the other hand has rather plain looks, probably the reason I can only find this one picture of it on the Internet.

Adult Willow Sawfly - Terry Gray
 This is a good time to say thanks to all the amateur naturalists and photographers who share their works.  Bob Barker and others like him put their photographs out under creativecommons.org, an organization which helps photographers put their work out for noncommercial use on sites like ours.  Many other photographers like Terry Gray have extensive portfolios which they allow us access to for the blog.  Thanks to all of you!

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