The True Bugs are notorious for the variety of scent glands. Many of the glands are used for defense- i.e. the bugs smell bad and your hand will smell bad if you handle them. The bad odor is accompanied by a bad taste, so the glands can convince predators to leave them alone.
The Wheel Bug, Arilus cristatus, is a large predator. Like all true bugs, it has sucking mouthparts in the form of a beak that can pierce prey, inject them with digestive enzymes and ingest the liquified tissues. Wheel bugs are commonly found hiding on flowers for insect pollinators that are attracted to flowers.
Our Butterfly Encounter yesterday (July 21, 2012), featured a photo workshop in the morning. We found this large wheel bug (picture below) and tried to maneuver it (carefully because they can bite) into a better pose. In addition to other scent glands, it possesses a bright orange rectal gland at the end of its abdomen. When prodded with a finger, the wheel bug would sometimes respond by everting the rectal gland. This behavior happens rapidly. The gland is only everted for a few seconds, making a well-focused picture challenging. After several bouts of everting the rectal gland, the wheel bug left for a more peaceful location. The picture below is the best I could get.
The rectal glands are only present in females. The odor is “sweet and pungent”. The odor and the bright orange color are warnings would be to predators. Why is the gland only in the female and why on the tip of the abdomen? Could the glands be used to add a protective odor to wheel bug eggs?