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133 The Bitter Taste of Success A blister beetle has blundered into a spiderweb, and now it waits, suspended in silk, for the spider to come and release it. The beetle dangles upside down, its bulbous wing covers hanging inverted. Their red and black chevrons announce that this insect dares to fly in the face of danger and survive. The beetles are clumsy and slow, but they are survivors nonetheless. Their members have steadily expanded the beetle niche, which now includes even open territories dominated by aggressive insectivores such as the birds, the mantids, and the orb spiders. The beetles have followed an unusual pathway to success. They have abandoned defense through speed and evasion, retreating instead behind the protection of an unwieldy shell. That shield created a niche for them that amalgamates the strategies of the two insect archetypes—those that fly and those that crawl. The beetles can spread their wings and venture as far as the wind may carry them. Then they can stow those wings and dive into thorns, wedge their way beneath sappy splinters of bark, dig into the leaf mold—excursions that would destroy the diaphanous membranes on the backs of other types of flying insect. Beetles have discovered that incorporating the lifestyle of a creature that crawls with that of one that flies provides them access to much more living space than can be occupied using either strategy singly. When they touch down, the beetles raise their antennae to gauge the local aromas, flavors, and vibrations. They have exploited their combination lifestyle to the fullest by sharpening their chemical senses—perfecting their command of the scents surrounding them and developing the potential of the chemistry within them. Their rigid body makes them passive, near-sighted, and slow to take wing—characteristics that would seem to preclude their living in the wide-open spaces patrolled by large, visual hunters. But as the beetle species have diversified into more and more habitats, their internal, defensive chemistry has allowed them to expand their range from the concealment of shelter or darkness into the most exposed sun field. 134 As it twists in midair, the blister beetle struggles ineffectually against the spider’s sticky strands. A single thread entangles its spiny back legs, and where they poke against each other, both legs bleed. The silken landing caused no injury, but this beetle is a reflex bleeder—translucent amber droplets bead on the leg joints. The blood contains cantharidin, which blister beetles synthesize in their own cells. The bleeding is a defensive response not detrimental to the insect, serving only as a reminder of the virulence of its blood. Cantharidin is a blister agent. Predators back away when they contact blister-beetle blood. Spiders cut blister beetles out of their webs and drop them if they sense it. The beetle is too poisonous to eat, so it is protected from those who have experienced its scent. Hungry birds ignore blister beetles; ants are repelled. Cantharidin can be irritating or severely toxic to mammals, depending on the dose. Spanish fly is not a fly but a beetle—a blister beetle— and cantharidin is the active ingredient of potions derived from Spanish fly extract. Its abuse has had debilitating and even lethal consequences time and again over the course of human history. Their chemical repellency gives otherwise defenseless beetles the capacity to occupy highly visible niches with impunity. Many of the beetles encountered by day are brightly colored. The color is a warning, indicating that the wearer bears a protective chemical defense. The milkweed beetles, either a crimson red or an iridescent blue black, are left unmolested on their sunny feeding grounds—their color is a reminder of their noxious taste. Ladybugs (not bugs but beetles) pursue aphids in their colonies on the exposed ends of shoot tips. Their warning coloration—orange and black like the monarch (who also feeds on milkweed)—advertises their unpalatability to all who notice them. These day-flying beetles have won places on the list of the hundreds of thousands of beetle success stories. They depend on their toxins for their safe passage and invest their energies synthesizing those defensive chemicals , or recovering them from the plants they feed on, or acquiring them by other, still more inventive means. Soon, the blister beetle continues on its way, preening off the last shards of spiderweb, resuming a quiet life, senescing a few weeks later and dying a natural death. Then, male members of another family of...

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