There are over 50 000 species of weevil world wide, 1 200 in Europe, and 475 in Britain. Many are considered pests, e.g. the vine weevil, left, the granary weevil (below), the cotton boll weevil, the grain weevil and rice weevil. Although palm weevil grubs are considered a delicacy in the islands of the South Pacific.
All Curculionids are vegetarian - mainly on plants, but a few eat fungus, and just a few are predatory. The females lay their eggs inside a plant by biting a hole first, or on their foodplant. Most adults have the characteristic snout (also called the rostrum) with jaws at the end, and elbowed, clubbed antennae extending from the snout (see left and below) usually with 11 segments. Adults range in length from 1 - 40 mm. The larvae (below left) generally live in plants are are usually short, round, fleshy, legless and milky coloured.
The adults generally feed on the outside of plants. Many are decorated with colourful scales which tend to rub off with age.
On the left is Otiorhynchus sulcatus, the vine weevil. It belongs to the Curculionidae family. The adults are dull black with small patches of dirty yellow on the elytra. The adults are flightless. The adults range in size from 8.0 - 10.5 mm.
They are slow moving and usually active after dark. Sometimes an adult will be found on the inside of a closed window when you get up in the morning. This probably means that you have an infested indoor pot plant. If you re-pot the plant you may find 10s - 100- of fat grubs. Don't throw them out. Put them in a dish and leave them out for the blackbirds - they love them! The larvae feed below the soil surface and the adults eat the leaves. Most vine weevils are females and they can reproduce parthenogenetically - so no need for a male or sex. The eggs are usually laid on the soil surface. Ground beetles are a major predator, as are commercially available nematodes.
On the left is Phyllobious sp. another weevil. Like many weevils it is covered in colourful scales. These can wear off with age leaving black patches.
Smith, L. (2014). Characteristics of the insect orders. Amazon. Characteristics of the insect orders with drawings and photographs to help you understand the differences between the different types of insect, and identify which order an insect is in, as well as fast facts about each insect order, and links to web pages with more detailed information.
Many orders have separate sections about the life cycle of the insect as well as its habitat requirements, and fossil history.
On the right is an adult granary weevil or grain weevil, Sitophilus granarius. It is a pest of stored grain, and its body length is 2.3 - 3.5 mm. Adults emerge from a grain, then mate - they cannot fly, so a mate is found by walking. The female drills a hole in a grain and lays a single egg, then plugs up the hole. The egg hatches and the larva begins to eat its way through the grain. It pupates inside the grain, and then emerges as an adult to start the cycle again.
A female can lay up to 250 eggs at a rate of 2 - 3 a day. The length of life cycle depends on temperature, but is 30 - 40 days in summer and 120 - 150 days in winter. A single breeding pair can give rise to over 6000 beetles in a single season if the conditions are right. In the U. K. it cannot breed outside.
Sitophus granarius is sometimes placed along with some other grain weevils in a separate family called Dryophthoridae or Rhynchophorinae.
On the left is Phytobius waltoni, a tiny, 2 mm long, aquatic weevil that lives on aquatic plants.
Hylobius abietis, the Pine weevil, Large pine weevil, and spruce weevil
Below right is an adult Pine weevil, also sometimes called the Large pine weevil or Spruce weevil. The body length is from 8 - 14 mm. It is common in Scotland, but less common in England. Adults are seen mainly from April to June. Females lay eggs on pine and spruce roots, although they can also eat larch. The adults prefer trees less than 6 years old, and can cause the death of a young tree, so are considered a pest.
The photograph on the right is a close-up showing the long, yellow, hair-like scales on the elytra.
The larvae feed on the inner bark and then the sap wood, and pupate inside the tree. They can grow up to 18 mm long.