Each year at this time things get a little bit spooky and we recognize a few styling bugs dressed in Halloween color (see Bugs in Orange and Black, October 31, 2005). This year’s ensemble features four insects that spent the summer and autumn on a few milkweed plants growing in my front flower bed. The first featured creature is a delightful insect called the milkweed leaf beetle. This beetle is a relative of the dogbane leaf beetle we met in “Gold in the Meadow”. Adults and larvae of this gorgeous insect eat leaves of milkweeds. Beetles first appeared in mid summer and removed large slices of the leaves of my milkweed. After dining for a few days females laid eggs that hatched into rather handsome larvae. These tiny orange cows grazed on my plants until late summer, then dropped to the earth to form pupae in the soil. By September a fresh batch of adult beetles had emerged and colonized the milkweed to fatten up on tasty leaves before finding a protected refuge to spend the winter somewhere in my garden.
In a society where everyone is or will soon be a momma, populations of oleander aphids explode.
Long beaks enable nymphs of milkweed bugs to eat seeds within the milkweed pod.
About the same time leaf beetles moved in I noticed a few colorful aphids on the stems of my plants. These interesting orange aphids with black legs, antennae, and cornicles (strange, small appendages on their abdomens) are known as oleander aphids. We think that oleander aphids originated in the Mediterranean region and traveled to this country with their host plant - oleander. They are common in the warm southern and western states where oleander thrives, but in cooler latitudes oleander aphids make their home on several types of milkweeds in fields and gardens. The ability to give live birth and the elimination of males allows a few oleander aphids to generate a bazillion daughters and granddaughters in just a few weeks. Like their relatives the rose aphid, they are attacked and killed by a host of predators and parasites (see “Murder and Mayhem in Aphid Land” (LINK) May 8, 2006,). As the blossoms of my milkweed turned to seeds, adults and nymphs of milkweed bugs were regular guests in my garden. Adult milkweed bugs insert stout beaks through the leathery cover of the seed pod and secrete digestive enzymes into the enclosed seeds. The liquefied meal is sucked up the beak and into the gullet where it is digested and used for growth, development, and the production of eggs. Eggs laid on the surface of the plant hatch into small orange and black milkweed bug nymphs. Like their parents, they too eat seeds of the milkweed.
The most dramatic denizen of my milkweed patch was the wonderful monarch butterfly. Although I never witnessed the laying of the royal eggs or the royal birth, I did discover three monarch caterpillars in early September. The larvae snipped leaf veins and consumed great portions of leaves. Later the larvae vacated the milkweed and formed chrysalises on a nearby chrysanthemum. With cold weather fast approaching I was relieved to see the monarch butterfly emerge one bright autumn morning. After climbing into the sunshine and allowing his wings to harden for more than an hour he took flight to find a source or nectar before beginning a journey of several hundred miles to spend the winter in the forests of Mexico (see “The royals are in the house”, (LINK) August 8, 2005). Why is milkweed the perfect plant for attracting so many bugs in orange and black? From the leaves and milky sap of the milkweed insects obtain potent defensive chemicals known as cardiac glycosides. These compounds are stored in the bodies of the bugs. Birds are important predators of many kinds of insects including butterflies and beetles. Cardiac glycosides found in the insects cause would - be predators such as blue jays to vomit vehemently. The conspicuous orange and black colors of the denizens of milkweed serve as a warning. Those attempting to eat these attractive morsels will get more of a trick than a treat. So, avoid eating bugs in orange and black and you should have a Happy Halloween!
References
To learn more about insects found on milkweed, please visit the following web sites:
http://www.texasento.net/Labidomera.htm
http://creatures.ifas.ufl.edu/orn/shrubs/oleander_aphid.htm
http://www.ivyhall.district96.k12.il.us/4TH/KKHP/1INSECTS/milkweed.html
http://www.monarchwatch.org/