Naturespeak A naturalist's view of the world

December 28, 2010

Winter in the Bag

Filed under: Uncategorized — wykes @ 9:01 pm

At first glance, the line of Blue Spruce trees bordering the parking lot of a local Walgreen’s Drug Store appeared to be decorated for the season. Pendulous spindles adorned each branch in a rustic, but tasteful, manner. “Ah,” I thought, “some refreshingly understated décor, how…how… refreshing.” Pointing this out to my infant daughter, I said something about Santa and his elves adorning every tree in town just for her. We were doing some last minute Christmas shopping and any excuse to extend the magic of the season was welcome.

Yes, this magic moment lasted for exactly three and 1/2 seconds as I suddenly remembered that my daughter was no longer an infant, but a full grown school teacher with a career of her own. She was in town for the holiday and we were running some last minute errands.  Instantly changing my intended statement in mid sentence, I recovered and pointed out the decorations for what they really were: bagworm sacs. Although she didn’t squeal with delight, she dutifully reacted with interest.

True, the term “bagworm sacs” doesn’t roll off the tongue like “Santa’s special ornaments” but that doesn’t make them any less interesting. These trees were heavily decorated around their lower branches as if an army of short people did the tree decorating (elves?). I will, for the balance of this discussion leave behind the reality that bagworms (the sac makers themselves) are considered pests in most circles. This would further denigrate them in my infant…er, my adult daughter’s mind. I’d have to call them “Little disgusting pest bags” and we’d both have to scream in mock disgust: “Eeee-yew.” Under the influence of this mindset, we’d be looking at an infestation rather than a decoration.

Bagworm sacs are spindle-shaped bags constructed of silk and plastered with dead spruce needles (although they are known to eat just about any plant – over 100 food plants – they prefer evergreens). Each structure is secured to the branch with a silken tie and, depending on whether they were made by a male or female worm, are either empty or full of eggs. Sorry, I’m getting ahead of myself aren’t I. “Eeee-yew” I hate it when I do that. Bagworms, you see, are a type of moth that spends their larval period as a caterpillar within a mobile home. The larvae weave a silk bag which incorporates leaf bits as camouflage. They crawl about with their head and prolegs exposed and their hind quarters hidden within the bag. When threatened they withdraw into their raggety shelters to cover their location.

Sometime in late summer the mature caterpillars stop wandering about and tie their travel bags to a permanent location. In so doing they draw shut the larger open end of the bag like a purse. The smaller end has a narrow flexible opening and this is left unaltered. Encapsulated within this suspended chamber, they turn about to face downward and pupate. Eventually they emerge as adults in the early fall. The males, wasp-like creatures with clear wings, push their way out of the bag and fly off to seek the company of the females. The females, however, are wingless and are forced to remain within the confines of their bag. When the males find the females they mate with them through the narrow opening at the small end. (I would never never reveal this fact to my infant daughter).

The impregnated females lay their egg clusters within the bag before crawling out and dropping helplessly to the ground. She will lay upwards of 1,000 eggs. Both sexes die shortly after mating (although the males are able to visit with a few more bags before cashing it in!) All this means that by wintertime only the female bags will contain living material in the form of yellowish egg clusters. The male shelters will be completely empty or contain the empty pupal skins.

All that was left for us to do was to cut open a few of the Walgreen bagworm sacs to see what they contained. Of the five that were harvested, four contained only empty pupal skins and were therefore male chambers. The fifth was a female chamber but the pupae had been infected with a fungus so she never emerged.

There is nothing like an infected ornament to cause one to lose the Christmas spirit so I decided to leave the remaining 5,689 sacs intact. Too bad my infant daughter isn’t a science teacher because she could bring a bunch of these things back to her classroom and have the kids cut them open. “Eeee-yew” they would declare in synchrony.  My daughter is an orchestra teacher, so we couldn’t see any way to incorporate bagworms into the classroom setting unless it was to make them into tiny bagpipes or something. I’m still not sure how a 4-year old was able to earn a teaching certificate.

1 Comment »

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