They’ve been crawling all over the place — a banner year, it seems.
About an inch and a half long, these black caterpillars sport honey-brown and blond bristles, with tufts of black bristles fore and aft, and a row of black chevrons along the back. A little online research came up with “silver-spotted tiger moth” (Lophocampa argentata).
According to life-history details published on bugguide.net, these caterpillars hatched from eggs laid last July and August then fed for several months before overwintering in shelters they spun. They emerged from the shelters this spring to resume feeding and growing until time to metamorphose into adults. The adults will emerge from the cocoons later in the summer and disperse to mate and lay eggs before dying.
The transformation from caterpillar to adult moth takes place in a pupa that, as in most moths, is protected by a fibrous (or silky) cocoon.
Our human experience can warp our perspective, leading us to think our tactics are the most common. Not so in many ways -- including how our offspring develop. According details reported through a Scientific American article by Ferris Jabr (10 August 2012), perhaps as many as 60% of all animal species metamorphose. (That number is hugely influenced by the overwhelming number of insects in the count of animal species — around 80%.)
And while we humans think of the adult stage as the primary stage for an individual, many insects spend most of their lives as immature animals, dying soon after becoming reproductive adults. Silver-spotted tiger moths spend less than 10% of their lives as adults, compared to our 80% or so.
Inside the chrysalis/cocoon, the larva (a more general term for what a caterpillar is) will dissolve nearly all the larval tissues, except certain groups of seed cells. Those seed cells (called “imaginal discs”) then direct the reorganization of the caterpillar goo into butterfly/moth parts.
The adult stage is mainly about reproduction and moving around to spread the species. In fact, some insects, like the large and delicate crane flies (sometimes called “mosquito hawks”), don’t even have working mouthparts as adults.
What’s the advantage of having one stage of life so different from another? Apparently, the biggest plus is that the larvae and the adults don’t compete for food: the animals eat one thing during part of their lives and eat another thing during another part of their lives.
All the silver-spotted tiger moth caterpillars I found were going about solo, but they apparently can live together in large groups and can strip a section of branch in the conifer they’re feeding on. Though unsightly, such limited denuding is not usually a significant hazard for the tree.
On the plus side, when the moths exit their cocoons in month or two and start flying in search of mates, perhaps some will become food for the baby birds soon to hatch in the nest under my front porch roof.
Handsome caterpillars to bird food … At my house, that’s a good trade for a naked branch or two.
Giles is owner/operator of Wavecrest Discoveries, long-running nature guiding service on the southern Oregon Coast. For information on how to arrange an exploration of our fascinating natural history, contact Marty at firstname.lastname@example.org, or www.facebook.com/wavecrestdiscoveries Questions and comments about local natural history are always welcome. www.wavecrestdiscoveries.com