Native plants can be fantastic additions to landscapes and their use has increased dramatically in recent years. Many of our natives have advantages relative to plants from foreign shores. Natives are often better adapted to local conditions of temperature, rainfall, and soil type. Moreover, they have a long evolutionary history with a broad array of native animals including birds, mammals, and insects. Native plants are homes and feeding stations for many creatures, and as such, they provide a constant source of entertainment and interest to our landscapes. As demand for native plants grows, seed collectors busy themselves gathering fruits and nuts to propagate these noble natives. This week our friend Stephanie was on a mission to gather seeds of our native pin oak tree. Soon after the acorns were collected, dozens of creamy, white, legless grubs appeared in the bottom of the collecting bag.
Legless weevil larvae emerge form the circular holes in acorns and enter the soil in advance of winter.
At first glance this seemed like some incarnation of spontaneous generation – the appearance of life from non-life. However, on closer inspection, tiny, perfectly circular holes were visible on the hulls of many acorns. This was the work of the acorn weevil. Acorn weevils are remarkable creatures noted for their exceptionally long snouts. The magnitude of this appendage would make Jimmy Durante jealous. At the tip of the proboscis are jaws used by the weevil to cut a hole in the husk of the developing acorn while it is still attached to a branch in the treetop. Into this hole, she deposits eggs that hatch and release tiny grubs which eat the nutritious meat of the acorn. To keep her brood safe from predators that might enter the acorn, she plugs the egg-laying hole with a small bit of excrement.
The acorns weevil's proboscis is remarkable by any standard.
In autumn, when the acorns drop to the ground, fully grown larvae chew small holes in the husk to escape their oaken nursery. They enter the soil and burrow several inches underground. They may remain in the soil for several years before transforming into a pupa. In spring with the return of leaves to the oak and the production of a new crop of acorns, adult weevils emerge from the soil and climb to the canopy of the tree to feed and deposit a new batch of eggs. To observe these remarkable insects first hand, simply go outdoors to your favorite oak and collect a batch of acorns. Place these acorns in a container such as a pitcher or cooking pot filled with several inches of water. Acorns that sink are usually intact and unlikely to be infested. Those that float have airspace within and are likely to contain weevil grubs or other interesting bugs. Crack a few of these open and observe the grubs inside. If you are really ambitious and desire a glimpse of the bodacious adults, you might try placing infested acorns in a pot with several inches of soil. This will provide grubs with the necessary habitat to complete their circle of life. The pots can be placed outdoors to expose the grubs to natural conditions of temperature and rainfall. Cover the pot with a bit of netting and, who knows, in a few years, you may actually capture some fantastic beetles with exceptionally large schnozzolas.
References:
Bug of the week gives special thanks to Stephanie for providing the specimens and inspiration for this week’s story. To learn more about acorn weevils, please visit the following web sites.
http://insects.ummz.lsa.umich.edu/MES/notes/entnote20.html
http://www.uky.edu/Ag/Entomology/ythfacts/allyr/yf804.htm