One of the last things one might expect to see on a newly-exposed grassy field in the middle of March is a caterpillar crawling along. This would be unexpected because most moths overwinter as eggs or pupae inside cocoons, not as caterpillars (larvae). Most moths, but not all. Some species of moths overwinter as larvae (and adults).
Tiger Moths (and Tussock Moths) overwinter as caterpillars and pupate in the spring before emerging as adults during the summer. One member of the Tiger Moth group that is familiar to many is the Isabella Tiger Moth, known as the Woolly Bear (Pyrrharctia isabella) in its larval stage. Another member of this group that overwinters as a caterpillar is the Great Tiger Moth (Arctia caja). As early as mid-March you can find both of these caterpillars wandering in search of a protected spot where they will form hairy cocoons that surround and protect their pupal cases. The pictured Tiger Moth adult (Great or Garden Tiger Moth) bears the white geometric stripes that give the members of this group their common name.
Naturally Curious is supported by donations. If you choose to contribute, you may go to http://www.naturallycuriouswithmaryholland.wordpress.com and click on the yellow “donate” button.
The Isabella Tiger Moth typically has two broods during the summer. The caterpillars (Woolly Bears) in the first brood pupate and emerge as adult moths mid-summer. The second brood overwinters as caterpillars and pupate in the spring. The Woolly Bears we see crossing roads at this time of year are second-brood caterpillars in search of protective hibernation sites (hibernacula).
Old-timers predicted the severity of the coming winter by the relative lengths of the black and brown bands of the caterpillars when they became easy to observe in the fall – the longer the black sections and narrower the brown section, the harder a winter they were in for. In fact, this may have had some validity, as brown hairs (setae) are added to the middle band every time the caterpillar molts. Therefore, the older the caterpillar, the wider the brown band. If winter comes early, the caterpillar’s brown band would be relatively narrow due to the fact it didn’t have time to mature fully and develop a wider brown section before hibernating.
The adult stage of the Isabella Tiger Moth is often overlooked, due to the appeal of the larval stage. This tan moth, with a wingspan of 1 ½ – 2 inches, has tiny black markings on its wings. Male and female are sexually dimorphic and can be distinguished by the color of their hind wings. Males have yellow-pale orange hind wings while the hind wings of females are rosy. (Photo: Woolly Bear; photo inset: female Isabella Tiger Moth)
Naturally Curious is supported by donations. If you choose to contribute, you may go to https://naturallycuriouswithmaryholland.wordpress.com and click on the yellow “donate” button.