Ground Beetle- Coleoptera, Passalidae


Kingdom - Animalia
Phylum - Arthropoda
Class - Insecta
Order - Coleoptera
Family - Passalidae
Scientific Name- Odontotaenius disjunctus


The eggs of the ground beetle are laid in the soil or sometimes attached in clumps to leaves. It is usually about 1.4 mm diameter and 3.3 mm long. Inside the egg is an embryo that will evolve into a larva.


Beetle larvae can be differentiated from other insect larvae by their hardened, often darkened head, the presence of chewing mouthparts, and spiracles along the sides of the bod
y. As adults, most beetles have a hard, dense exoskeleton that covers and protects most of their body surface. The larva molts its skin as it grows into a new instar. Larvae normally go through 3 to 8 instars. Coleopteran larva have a well-developed dark in color head capsule with chewing mouthparts. Spiracles are spread out along the body which are used for breathing. Most have legs toward the front of the body and prolegs at the rear of the body.


When larvae reach their last instar stage, they molt their skin to transform into a pupa. Pupation for these beetles normally occurs in the soil and for some species it occurs in the food plant. The time length of pupation varies among species and is influenced by environmental influences such as climate and temperature.


external image anatom.ashx?w=450&h=285&as=1

They are shiny and black and measure about ranging from 20-43 mm in length. This beetle's head is narrower than than the pronotum, or the upper prothorax, and the mouthparts jut out forward and the antennae have 10 segments and the width of the segment just behing the head (prothorax) is usually narrower than the abdomen and they have a single "horn" on their head. The front wings, known as the elytra, are just as hard as the rest of the exoskeleton. They fold down over the abdomen and serve as protective covers for the large, membranous hind wings.

Identifying Characteristics

These beetles have a robust body and a gap between the pronotum and elytra which are deeply grooved. Also, they are toothed and their 10-segmented antennae are not elbowed but they are curved when relaxed. Also, their antennal plates cannot be pressed together as they can in related families/
robust body, distinct gap between pronotum and elytra.


Ground beetles are usually seen under stones, bark, logs and other debris laying on the ground. They live mainly in open fields, forests, along rivers, lakes, and ponds, and at the edges of marshes and bogs. Some species are considered as subaquatic.

Geographic Range

Most carabids occurring in the Mixedwood Plains Ecozone are terrestrial. They look for their prey at night and some species are attracted to lights. Larvae are commonly seen underneath debris. These insects are found in eastern and south-central North America. This particular beetle was found in Elizabethtown, North Carolina.
external image north-carolina-map.gif
external image Elizabethtown_NC.gif

Mating Behavior

There may be conflicts between males and females until only one of each is left, which ensures reproduction by the strongest and fittest. Male beetles are territorial and will fiercely defend their small patch of territory from intruding males. In such species, the males may often have horns on the head and/or thorax, making their overall body lengths greater than those of the females. Pairing is usually short but in some cases it will last for several hours. During pairing sperm cells are transferred to the female to fertilize the egg. Males and females mate at different times in their adult stage. Some species of the coleoptera only live for a few days where as others are able to live for over a year. Individual groups and species have evolved to enable more success in the production and survival of their offspring by advancements in their mating behavior.

Life Cycle

Winter is spent in the larvae or adult stage. The adults then grow to mate and disperse. Next they lay their eggs independently and the larvae hatch and go through several stages before pupating. Their eggs may be scatted in the substrate, attached to leaves, inserted in the food medium, or attached singly to the food source. The embryo develops inside the egg and will later emerge as a first instar larva. Their full development is usually complete in one year. The coleoptera beetles all undergo a full metamorphosis with egg, larva, pupa, and adult stages. To see the morphology of each stage of the lifecycle of this beetle, click here.
external image life-cycle-coleoptera-800X800.jpg

Feeding Habits

Members of the family Carabidae are feed on seeds of plants, such as oats, barley, wheat, corn, and parsley, but the damage done is usually insignificant. Decaying wood is also a main part of the diet of adult and larvae beetles. Another source of food for larvae is plants or their predatory instinct. They also feed on other insects as larvae and adults. All of them must eat the feces of the mature adults which are composed of wood that is fragmented, digested, inoculated with bacteria and fungi from the digestive tract of the adults, and further decomposed after being excreted.

external image img138.jpg

Ecological Role

external image 5_301373.jpg

Ground beetles are considered beneficial insects because they often act as "weed killers" by eating the infectious plants. They also feed on many harmful household and garden pests including cutworms, fly maggots, caterpillers, aphids, weebils, other beetles, slugs, and snails. Farmers sometimes even develop beetle banks to foster, protect, and care for the beetles so that they can protect and fertilize their crops.



To visit my educational glog about the coleoptera, here!