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Posts Tagged ‘behavior’

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Dog day cicada (Tibicen canicularis) photographed July 28, 2012 in our yard. Click/double click image to enlarge.

I recently became aware of a beautifully filmed and presented eight minute video regarding the periodical cicada (Magicicada septendecim) life cycle. “Return of the Cicadas” is as artistic as it is informative. Best of all, it is freely accessible via the Internet.

An additional resource worth checking out is Cicada Mania. Despite its name, this professionally presented resource is an exceptional compilation of regularly updated periodical cicada information. I was particularly pleased to see that Illinois is slated as one of three states that should experience a large-scale periodical cicada emergence in 2014. I’ve never experienced a massive emergence before, but plan to document as much as I can when it occurs!

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Seven legs and fully functional. The story follows. Click/double click image to enlarge.

Last night the smaller juvenile Honduran curly hair tarantula (Brachypelma albopilosum) molted. The molt began normally and nearly everything proceeded within a normal time frame of about an hour once the actual molting began.

Near the end of the molt, the distal half (part furthest away from the body) of the right hind leg  remained partially enclosed within the old exoskeleton. It seemed that slipping the last leg out of the old exoskeleton shouldn’t be a problem. After all, every molt I’ve observed up to this point had gone smoothly.

Because tarantulas are so soft-bodied and delicate while molting, I knew to leave the spider alone and let nature take its course. It was 2 AM. The worst case scenario might be loss of an end of one of that leg, which should regrow after the next molt. I went to bed.

This morning I awoke to a healthy, active, significantly larger spider with seven legs. The entire leg of concern was shed entirely sometime during the evening.

So, what happened? Bear with me on this, the photograph will tell the story, and it will all make sense.

I photographed and outlined the molting process last spring in an entry entitled “Juvenile Mexican red knee tarantula (Brachypelma smithi) molt sequence.”

After emerging from the old exoskeleton, the tarantula remains on its back for up to a half hour, alternately flexing and pulling the legs back in tightly as seen in the fifth and six images in “Nine image curly haired tarantula (Brachypelma albopilosum) molt sequence.”

The coordinated collective extension and contraction of the legs occurs as the spider pushes blood (hemolymph) into the legs, stretching them to a significantly increased length during that time period.

So, what happened during the six hours between 2 AM and 8 AM? And why did the spider shed the entire leg?

I think I can answer the first question anyway by closely examining the photograph below, taken several hours after the molt.

If you double-click the image, you will see the freshly shed, damaged previous exoskeleton with the partially thickened new leg held firmly in place.

Leftmost exoskeleton shed June 14, 2012. Center exoskeleton with retained leg shed July 23, 2012. Newly emerged, still enlarging Honduran curlyhair tarantula (B. albopilosum) photographed July 23, 2012. Double-click image for full impact.

The distalmost end of the retained new leg (part furthest away from the body) appears to have expanded, rupturing the part of the old exoskeleton that originally housed it. The tight ring of the original exoskeleton’s coxa and trochanter was too heavily reinforced to allow the next region of the new leg to expand, effectively trapping the new leg and preventing its expansion.

The regions of the new leg which had been closest to the body are clearly fully expanded, and the break between the coxa of the spider’s new leg and the remaining thickened trochanter, which has expanded to about 1/3 of the width of the original cephalothorax, is evidenced as an open wound at the proximal end of the retained leg.

Kind of gory, but not entirely unexpected.

Shedding of limbs, automy, is certainly not uncommon, as evidenced by the frequency by which we encounter arthropods missing legs.

Rainer Foelix, author of Biology of Spiders, states that one can easily induce a spider to perform automy by pulling or squeezing the femur, a region toward the middle of the leg. Interestingly, doing this to an anesthetized spider does not result in automy, leading to the conclusion that automy within spiders is a voluntary act.

Page 282 of Foelix’s book explains in detail why automy typically occurs at the joint between the coxa and trochanter (close to the body),  rather than a joint nearer the area of compression or damage. Essentially, the single muscle traversing the joint between the coxa and trochanter readily detaches itself from the trochanter and withdraws into the coxa. All other muscles in that area act together to close off the end of the coxa similar to the way that the lid closes on a small pedal-based, hinged-lid garbage can. Additionally, the hemolymph (blood) pressure forces the joint membranes to bulge forward, sealing the wound.

Leg automy occurs frequently in nature. In fact, samples of spiders typically show 5 to 20% of a typical field catch of spiders to be missing at least one leg. Most often this occurs in male spiders when an aggressive female tries to consume them, within seconds of a bee or wasp caught in a web successfully stinging the web’s owner in the soft membrane between leg joints, or when a spider is grabbed by a predator.

Another unexpected biology lesson arising from tarantula keeping!

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The black light set-ups were great for observing species diversity, as well as mating of numerous species. Rove beetles were present in particularly large numbers. Click/double click to enlarge.

Last night I stopped in during the “Night Bugs” program at the University of Illinois Pollinatarium. Staff and an array of volunteers set up three sheets with blacklights.

Microscopes were available for those who wanted to look more closely at insects of interest. Several entomologists were on hand to  help with identification and answer questions.

It was certainly a very nice, informative, congenial way to spend a few hours during a summer evening!

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Squash bugs (Anasa tristis) are significant agricultural pests during the summer and fall. They pierce leaves stems and fruits of melon and squash while feeding, wounding tissues which then collapse. Click image to enlarge.

Despite our best efforts in dealing with the drought, two of the zucchini plants suddenly collapsed yesterday.

Several squash bugs emerged from the compost at the base of the plants as we watered. We found several clusters of copper colored eggs on the surface of some of the leaves.

Squash bug eggs on the underside of a butternut squash leaf. Click image to magnify.

Because so many of the flowers were actively being pollinated yesterday morning, we waited several hours before spraying the plants, flowers, leaves and zucchini with Sevin.

This morning we found adults squash bugs on several of our massive butternut squash plant’s leaves. Turning over the leaves and stems revealed mating squash bugs, an ovipositing female, a large number of egg clusters, and several minute gray nymphs.

The bush cucumbers, which are bearing well, and the heavily flowering melon plants are unaffected at this point.  I am crushing the eggs, nymphs and adults as I encounter them.

We’re off to problem solve with some of the County Extension staff later today.

Mating pair of squash bugs (Anasa tristis) I encountered when I turned over the first butternut squash leaf squash leaf. Click/double click image to magnify.

Ovipositing female squash bugs (Anasa tristis) on the underside of the second butternut squash leaf squash leaf. Click image to enlarge.

Gray squash bug (Anasa tristis) nymphs on the underside of the first butternut squash leaf. Click/double click image to enlarge.

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Dense packing of oleander aphids leads to physical changes, such as the wing pads seen in some of these individuals. Click image to enlarge.

East central Illinois’ recent drought conditions have been particularly stressful on plants.

We typically find an abundance of field bindweed (Convolvulus arvensis) along our west and south fences adjoining the neighboring fields.

Heavy feeding and asexual reproduction of oleander aphids on the few surviving bindweed plants have resulted in aphid densities well beyond the norm.

The adult aphids, all female, are viviparous (giving birth directly to young, thus bypassing an external egg stage) and parthenogenic (meaning fertilization does not occur, so the progeny are clones of the adult female).

The offspring typically develop into wingless adults, though overcrowding and aging/stress of host plants can lead to production of winged adults. Note the development of wing pads on some of these young aphids.

It will be interesting to see how the bindweed is impacted over the next several days.

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Note the upright position of the original exoskeleton during the molt. Double-click image to enlarge.

The three, once tiny Mexican redknee tarantulas (Brachypema smithi) obtained in January continue to grow and develop at different rates. The smallest one molted for the second time Saturday morning.

Unlike previously observed molts, the tarantula did not turn over onto its back, but rather emerged from an upright premolt stance. I haven’t seen that before, though I have read that likelihood of emergence issues and likelihood of molting-related mortality increase when molting occurs in this position.

Emergence occurred over a thirty minute period, though part of the cephalothorax remains attached to the abdomen of the newly emerged tarantula 24 hours later. I observed the same issue in one of this tarantula’s siblings.

Double-click the middle and final emergence images to see the molt process in greatest detail.

Upright emergence led to a the spiderling balancing precariously for a moment. Double-click image to enlarge.

On its back, moving and expanding legs. The spider remained in this position for about a half hour before turning upright. Click image to enlarge.

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Note the long, distinctive yellow and black-banded legs characteristic of this species. Double-click to enlarge.

Stilt-legged flies (Rainieria antennaepes) are ichneumonid wasp mimics who walk with their front legs extended, appearing like wasp antennae. I have to admit that this fly did an excellent job of initially fooling me.

The adults feed on detritus and dung. The natural history of  this species is poorly understood.

There has been an abundance of these flies around the peony bushes and along the green house siding.

Stilt-legged flies (Rainieria antennaepes) exhibiting its characteristic body posture and extended front legs. Double-click image to magnify.

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