Broscus cephalotes is a species of nocturnal, coastal ground beetle found throughout most of Europe. Its range spans from western Europe into western Siberia. The species was introduced recently (circa 1975) in the eastern areas of Canada and has spread farther south and west into the United States. As a member of the family Carabidae, Broscus cephalotes is generally considered beneficial to humans due to its predatory habits. Their varied diet often includes crop pests and other small organisms.
Description
Broscus cephalotes has a dull black coloration, without any metallic hue, and it can be quite large: between 16 and 23 mm. The morphology of the beetle is similar to other beetles in its family. B. cephalotes is flightless and flatter than many other species of Carabidae, which helps it hide in close spaces (e.g. crevices under stones or under bark). Body shape and presence or absence of the ability of flight can provide clues to diet of beetles, but does not provide conclusive evidence. Although mouth-parts are a better indicator of the type of food consumed by the beetle, the best method of determining the diet of a beetle is gut dissection. The asymmetric mandibles of B. cephalotes are blunt and twice as long as they are wide. The mandibles are curved to a rounded point at the end, with the left mandible is slightly longer and wider than the right mandible. These mandibles are multi-purpose tools. The beetle uses them to create and maintain the tunnels in which they spend most of their lives. The opened mandibles can act as shovels or pull dirt and debris from the walls of their tunnels and deposit it outside the burrow. Additionally, the mandibles can act as shovels in the loose sand of the beetles’ coastal habitat. Another critical use of the mandibles is in feeding, as discussed below.
Feeding
Broscus cephalotes are primarily carnivorous beetles; however they will consume a wide variety of food. They are generalists, and the adults do not discriminate much in what they consume. A recent study showed that B. cephalotes in laboratory conditions will attack everything that runs across the opening of its burrow, though they preferred to attack and eat woodlice and ants. Some of what has been found in various beetles’ digestive tract include: plant material and various types of insects: ants, wolf spiders, Aphididae, caterpillars, Diptera, Acarina, Bibionidae, Coleoptera, adult Lepidoptera, and Heteroptera. However, there has been no evidence of cannibalism in this species of beetle. The diet of the larvae of this family has not been as widely studied because the larvae spend their time in tunnels and are difficult to identify even when not hidden in the soil. Carabidae larvae are usually more carnivorous than adults and have a more restricted diet. The limited diet may be due to their subterranean habitat and their small size. Additionally, the larvae of Carabidae beetle tend to be fluid feeders, regardless of their status as adults.
Broscus cephalotes has two main methods to detect prey: tactile cues and olfactory cues. The olfactory cues, however, do not seem to be very specific, as the responses to the cue do not correspond strongly to preference of prey. The beetle, once in possession of its prey, holds the organism with its forelegs and tears off pieces of the organism to consume. The mandibles are used to tear open the cuticular structures of its meal and expose the soft tissue areas within the organism. Fluid is produced in the mouth during feeding that causes the discoloration of flesh and begins the digestive process. This fluid is composed of a variety of enzymes that begin the digestive process before the prey has entered the beetle’s digestive tract. Many samples of B. cephalotes were found to have sand in their digestive tract in addition to prey. Sand in the digestive tract may help the beetle grind up the tougher parts of the prey, although it has not yet been determined if the sand is ingested for this purpose.
Habitat and habits
Broscus cephalotes can be found all across temperate western and central Europe, extending into western Siberia. Specimens are usually found in the coastal regions, but can also be found more rarely inland. It generally can be found in the vegetated dunes on the coast, but prefers the more sparsely vegetated areas.
The first appearance of B. cephalotes in North America was recorded in Nova Scotia in 1978. It seemed as though the species was well established in the area at the time, but still a relatively new arrival. The species is still confined to the eastern seaboard in North America and is less common than in Europe.