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Elaiosomes

Male Walkingstick Cerci

Congratulations to Sharon Weizenbaum, Beth Herr and David Ascher for correctly identifying the Mystery Photo as the tip of the abdomen of a Common Walkingstick (Diapheromera femorata), also known as Devil’s Darning Needle, Devil’s/Witch’s Riding Horse, and Prairie Alligator due to its unusual shape.  While the Common Walkingstick is a mere 3” long, the largest North American species can grow to 7” and one tropical species may reach 14”.

The Walkingstick lives up to its name – it is easily mistaken for a twig with its slender body and legs.  By remaining motionless during the day (or gently swaying in the wind like a leaf or twig would), and feeding on the leaves of various deciduous trees at night it avoids many predators with its physical and behavioral adaptations. The practice of using both camouflage and mimicry is referred to as crypsis.

Both the male and female Walkingstick possess a pair of appendages at the tip of their abdomen known as cerci.  The cerci on a female are short and straight, while those on the male are longer and curved.  They are sensory organs, but in addition, the male uses his cerci to grasp the female when mating with her (see inset).  According to entomologist Dr. Gilbert Waldbauer, the cerci are very effective, allowing the male Walkingstick to clasp the female for many hours (weeks for some species) in order to prevent another male from mating with the female.

This is the time of year you are most likely to notice Walkingsticks, as this is when they are maturing and reproducing. Females drop their eggs to the ground from the canopy and because a portion of the outside (capitulum) of each egg is edible (like the elaiosomes of many spring ephemerals), ants carry the eggs below-ground to their nests and eat the capitulum, leaving the intact eggs to hatch and develop.

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Red Trillium Seeds Being Dispersed By Ants

9-10-15 red trillium fruit and seeds  092The flower of Red Trillium (Trillium erectum), also known as Stinking Benjamin and Wake Robin, is familiar to many, as it is one of our more common spring ephemerals. The three reddish-maroon (some populations have white, yellow-green, or paler red) petals of its flower are colored and smell faintly like rotten meat. Lacking nectar, these flowers rely on deception to bring in pollinators which are primarily flies and beetles that are typically attracted to dead animals.

Once a Red Trillium flower is pollinated, the Hershey Kiss-shaped red fruit begins to develop. The seeds of Red Trillium have oily appendages called “elaiosomes” which attract a number of insects, particularly ants. These elaiosomes (also called “ant snacks”) contain lipids and protein highly sought after by ants. The ants carry the seeds down into their underground tunnels where they feed the elaiosomes to their larvae and dispose of the seeds in their compost pile. Here they they put their droppings, or frass, as well as dead ants. Conditions for germination are ideal in such a spot, and, in fact, research shows a greater germination rate for seeds with elaiosomes than those without them.

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