The longhorn beetles (Cerambycidae), also known as long-horned or longicorns (whose larvae are often referred to as roundheaded borers), are a large family of
beetles, with over 35,000 species described.[2]
Most species are characterized by
antennae as long as or longer than the beetle's body. A few species have short antennae (e.g., Neandra brunnea), making them difficult to distinguish from related families such as
Chrysomelidae. "Cerambycidae" comes from a Greek mythological figure: after an argument with nymphs, the shepherd
Cerambus is transformed into a large beetle with horns.
Longhorn beetles are found on all continents except Antarctica.[3]
Description
Other than the typical long antennal length, the most consistently distinctive feature of adults of this family is that the antennal sockets are located on low tubercles on the face; other beetles with long antennae lack these tubercles, and cerambycids with short antennae still possess them. They otherwise vary greatly in size, shape, sculpture, and coloration. A number of species mimic
ants,
bees, and
wasps, though a majority of species are
cryptically colored. The
titan beetle (Titanus giganteus) from northeastern South America is often considered the
largest insect (though not the heaviest, and not the longest including legs), with a maximum known body length of just over 16.7 cm (6.6 in).[4]
Larvae are 0.5–22 cm (0.20–8.66 in) long, elongate in shape and lightly sclerotised. The
prothorax is often enlarged and the sides of the body have lateral swellings (ampullae). The head is usually retracted into the prothorax and bears well-sclerotised mouthparts. Larval legs range from moderately developed to absent. The
spiracles are always annular.[5]
Biology
Diet
All known longhorn beetle larvae feed on plant tissue such as stems, trunks, or roots of both herbaceous and woody plants, often in injured or weak trees.[6] A few species are serious
pests. The
larvae, called roundheaded borers, bore into
wood, where they can cause extensive damage to either living
trees or untreated lumber (or, occasionally, to wood in
buildings; the
old-house borer, Hylotrupes bajulus, is a particular problem indoors).
Many longhorns locate and recognize potential hosts by detecting
chemical attractants, including
monoterpenes (compounds released en masse by woody plants when stressed),
ethanol (another compound emitted by damaged plant material), and even bark beetle
pheromones. Many
scolytine weevils share the cerambycid's niche of weakened or recently deceased trees; thus, by locating scolytinids, a suitable host can likely be located as well. The arrival of cerambycid larvae is often detrimental to a population of scolytinids, as the cerambycid larvae will typically either
outcompete them with their greater size and mobility, or act as direct
predators of them (this latter practice is less common, but has been observed in several species, notably Monochamus carolinensis). Cerambycids, in turn, have been found to play a role in attracting other wood-borers to a host.[7] Borgemeister, et al. 1998, recorded that cerambycid activity in girdled twigs released
volatiles attractive to some
bostrichids, especially Prostephanus truncatus.[8] A few cerambycids, such as Arhopalus sp., are adapted to take advantage of trees recently killed or injured by
forest fires by detecting and pursuing smoke volatiles.
Pollination
In addition to feeding on other plant tissue, some species feed on pollen or nectar and may act as pollinators. Assessing the efficacy of beetle pollinators is difficult. Even if pollination of one species by beetles is shown, that same beetle may also act as a flower predator toward other species. In some cases, beetles may act as both pollinators and predators on the same flowers.[9]
Flowers specializing in pollination by beetles typically display a
particular set of traits, but pollination by longhorn beetles is not limited to these cantharophilous flowers. A review of angiosperm pollination by beetles shows that Cerambycidae, along with Curculionidae and Scarabaeidae, contains many taxa that are pollinators for not only specialist but also generalist systems.[10]
Beetles in the New Zealand genus Zorion are known to feed on pollen and have a specialized structure similar to that of
pollen baskets found in bees.[11] Species in this genus are thought to be important pollinator species for native plants such as
harakeke.[12]
Some orchid species have been found to be largely reliant on longhorn beetles for pollination. The species Alosterna tabacicolor was found to be the main pollinator of a rare orchid species (Dactylorhiza fuchsii) in Poland.[13] Another rare orchid Disa forficaria, found in the
Cape Floristic Region in South Africa, relies on the species Chorothyse hessei for pollination. D. forficaria uses
sexual deception targeting male C. hessei, possibly indicating a long history of
co-evolution with longhorn beetle pollinators.[14]
The proportion of longhorn beetle species that act as pollinators is unknown. The fact that two species of longhorn species from distinct subfamilies (
Lepturinae and
Cerambycinae) found on different continents both with significant roles as pollinators could suggest that some capacity for pollination may be common among longhorn beetles.
As with many large families, different authorities have tended to recognize many different subfamilies, or sometimes split subfamilies off as separate families entirely (e.g.,
Disteniidae,
Oxypeltidae, and
Vesperidae);[16] there is thus some instability and controversy regarding the constituency of the Cerambycidae.[17] There are few truly defining features for the group as a whole, at least as adults, as there are occasional species or species groups which may lack any given feature; the family and its closest relatives, therefore, constitute a taxonomically difficult group, and relationships of the various lineages are still poorly understood.[18] The oldest unambiguous fossils of the family are Cretoprionus and Sinopraecipuus from
Yixian Formation of Inner Mongolia and Liaoning, China, dating to the
Aptian stage of the Early Cretaceous, approximately 122 million years ago. The former genus was assigned to the subfamily
Prioninae in its original description, while the latter could not be placed in any extant subfamily.[19][20]Qitianniu from the mid-Cretaceous
Burmese amber of Myanmar, dating to approximately 100 million years ago, also could not be placed in any extant subfamily.[21]