Tuesday, September 3, 2013

Female Instincts

This elegant and docile looking nectivorous wasp is also a vicious predator who will slay spiders more than twice her size in order to insure the success of her children.  Also known as a tarantula hawk or spider wasp (Pepsis thisbe), these huge wasps grow up to two inches (5 cm) long from the powerful jaws to the tip of their glossy black abdomen.  Females can be identified by the curled tips of their antennae, while male antennae are straight. Both are commonly seen sipping nectar from a variety of flowers, and are especially fond of milkweeds. But only the female possesses a sharp stinger and the instinct to use it to deliver powerful neurotoxins to stun food for her offspring. Unless you harass her, there is very little chance that a tarantula hawk would attack a human. But if you are a tarantula, she will chase you down.

We were fortunate to witness the aftermath of such a biochemical attack along the Upper Salt River  last weekend. While walking along the road to our camp, we noticed a tarantula splayed out in the dirt. I poked it with my toe, but it didn't move. Within moments, a tarantula hawk started circling the spider, so I stepped away, and she landed on top of it and began to drag it up the hillside. We think she must have already delivered the neurotoxin that effectively paralyzes the prey, and was returning to retrieve it  once it was completely immobilized. Unperturbed by our presence, we watched as she pulled the spider up beneath a rock. A single egg will be buried with the zombified spider, providing nutrition for wasp larvae as it develops into a two inch long grub, eating the spider alive as it grows. After the larvae has had its fill, it will pupate and remain in a resting stage underground for several months before emerging as an adult wasp. 

I like knowing that for every tarantula wasp, there was once a big hairy tarantula walking the earth. We see a lot of wasps around, so that must mean that there are is an equally healthy population of tarantulas in the neighborhood.  

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