Showy Insects and Spiders of Autumn

*Note: this article was originally written in September 2017 and printed in the Nantucket Inquirer and Mirror in the November 30, 2017 issue

Fall is finally here. The air is cooling down and drying out, the tupelo trees are turning red and the goldenrods and blazing stars are blooming in all their yellow and purple splendor. With all the fall wildflowers in peak bloom, now is a great time to take a quiet walk in Nantucket’s sandplain grasslands to enjoy the display of color and catch a glimpse of some showy fall insects too.

Of course, the star of the show has to be the Monarch Butterfly. In recent years, we’ve noticed an alarming drop in the abundance of these regal butterflies, but this year, we are encouraged by what seems like quite an uptick in the number of monarchs flitting through the grasslands and shrublands on island. Monarchs arrive on Nantucket by mid-summer and lay their eggs on milkweed plants. Tiny yellow, black and white striped caterpillars emerge and immediately get to work munching on the milkweed. They eventually pupate in to a green chrysalis, and the adult emerges as the familiar orange and black beauty. While the butterflies that arrived here earlier in the summer will die as they only live, on average, 2-5 weeks, their offspring, the adults that we see now, just completed their metamorphosis and will live for up to 9 months. It is these adults that will soon begin their long migration south to wintering grounds in the mountains of central Mexico. Migration on this scale is quite unusual in the insect world and is only known in a few species of beetles, dragonflies, grasshoppers and locusts.

 

 

Another very common insect at this time of year is the larval form of the Flannel Moth. Right now, we are seeing Flannel Moth caterpillars all over black huckleberry leaves in the coastal heathlands and shrublands. These caterpillars are quite conspicuous and easily recognizable. The inch long larvae are covered in long hair-like setae, resembling a Persian cat. Thus, some members of the genus are nicknamed “puss caterpillars.” The caterpillars start out covered in wispy white fluff, but by the end of summer their coloration changes after they shed their skin to grow, and molt to a brownish-tan color. They may look soft and cuddly, but the long soft hairs on these caterpillars conceal hollow spines that contain venom. If you rub against these spines, the resulting sting can cause skin irritations that range from mild itching to painful blisters. So, look but don’t touch these fluffy little caterpillars. Flannel moth caterpillars are usually sparse, but in the summer of 2008, a few areas of the island experienced a major outbreak of these caterpillars as well as a Chaindot Geometers and Io moth caterpillars. That summer, caterpillars completely defoliated huge areas of shrubland. We haven’t seen a caterpillar outbreak quite like that since and all the shrubs recovered from the defoliation with no problem.

Another creature that is very easy to observe and common in the grasslands now is the Yellow Garden Spider, or Writing Spider (Argiope aurantia). The large size of this spider is impressive and certainly gives one pause, but it is harmless to humans as they rarely bite and if they do, the venom is mild with little more than a welt as a reaction. They are orb web weavers and tend to build their webs close to the ground in gardens and tall grassy areas. The web itself is distinct as it is large (approximately 2 feet wide) and the spider builds a thick, zigzagged line of silk in the center of the web, called a stabilimentum. You might guess from the name of this structure that it has a stabilizing affect for such a large web, but many biologists dispute its purpose, suggesting that perhaps it actually camouflages the spider sitting in the center of the web, lures prey in to the web, or warns birds of the presence of the web to deter them from flying in to it. Whatever the purpose, the spider takes down this central part of the web on a nightly basis and constructs a new one. Spiders may not be everyone’s cup of tea, but I think most could, from afar, appreciate the beauty of this arachnid.

 

We highly recommend a walk through the Nantucket Conservation Foundation’s Head of the Plains property or the Nantucket Land Bank’s Smooth Hummocks property in the fall. Both of these properties contain excellent examples of the globally rare sandplain grassland and heathland vegetation communities. Multiple species of goldenrod, New England Blazing Star and many varieties of white and purple asters are all in peak bloom right now and are attracting many species of butterflies and other insects. Now that the island has quieted down, it’s a great time of year to enjoy the peace of these properties and see some of the less appreciated species of wildlife on Nantucket.

The Nantucket Conservation Foundation is a private, non-profit land trust that depends contributions from our members to support our science projects, conservation property acquisitions and land management efforts. If you are not already a member, please join us!  www.nantucketconservation.org