By Scott Solomon, Rice University
Insects have adapted to their ecosystems and lifestyles through the process of evolution. A familiar example to most pet owners is the flea; they are supremely well adapted as parasites. Another example is dung beetles; they feed on animal dung and the females lay their eggs in balls of dung that they bury underground, creating a safe place for their larvae to emerge and feed until they grow into adults.
Importing Dung Beetles into Australia
The Australian cattle industry is big business, but by the 1960s a problem had emerged that could no longer be ignored. The waste produced by Australian cattle herds was accumulating, leaving fields of cow patties where the grass became fouled and inedible. As much as 20% of cattle pastures were rendered unusable each year, and because it could take years for an individual dung pile to decompose, the problem was getting worse each year.
Elsewhere in the world, the accumulation of cattle dung was much less of a problem, thanks in large part to the activities of dung beetles. While there are more than 400 dung beetle species native to Australia, they evolved to be able to process and feed on the dung produced by marsupials like kangaroos and wallabies. But the dung produced by these native Australian mammals consists of dry, coarse pellets. When cattle were introduced to Australia beginning in the late 18th century, the native dung beetles could not process the large, wet patties made by the introduced cattle.
The solution was to import dung beetles from other parts of the world that are better equipped to bury and consume cattle waste. 43 species were released between 1965 and 1985.
In an effort to cover as many regions and seasons as possible, the chosen species were selected because they varied in terms of their habitat preferences and the time of year in which they are active. Of the 43 released, 23 species had become established by 2018. The program was a success—studies found that the introduced dung beetles increased the production of pasture grass by about 1 ton per acre.
This article comes directly from content in the video series Why Insects Matter: Earth’s Most Essential Species. Watch it now, on Wondrium.
Natural Waste Recyclers
Dung beetles belong to the Scarabaeidae family, commonly known as scarabs, one of the most diverse families of beetles with over 30,000 described species. They have several anatomical features that make them well suited to their role as waste recyclers. They are compact, with stout bodies and short antennae.
The faces of scarab beetles are broad and flat due to an enlarged clypeus, located just above the mouth. The clypeus extends over and protects the mandibles and has a jagged lower edge that serves as a digging tool and rake for scraping and sorting through dung.
The tibiae on the front pair of legs are enlarged and serrated in many scarab species to serve as an additional pair of digging tools. The dung beetle uses these front legs to scrape dung under its body, where the other pairs of legs form it into a ball. The hind pair of legs have pointed tarsi that are used for holding the ball as it is rolled away to be buried.
Fleas: The Parasites
Fleas are supremely well adapted as parasites. Their mouthparts are well suited to feed on blood from their hosts. The two maxillae, along with a specialized structure called the epipharynx, found only in fleas, form three stylets that puncture the skin. The epipharynx is then inserted into a capillary and acts like a straw to suck up blood.
Saliva containing anticoagulants is produced in the flea’s salivary glands, which are connected by a short tube to its mouth and excreted into the wound to keep the blood flowing while the flea feeds.
Many fleas have comb-like spines that help keep them on their host by allowing hair or fur to get caught between the grooves. This way, even an aggressively scratching dog or cat will have a hard time dislodging the flea from its body.
Fleas also have bodies that are flattened from side to side. This compressed body, along with a reinforced exoskeleton, makes it very difficult to squish a flea even if you do manage to dislodge it.
The Jumping Ability of Fleas
Fleas do not have wings but are able to jump long distances—as much as 8 inches high, the equivalent of 66 times their body length. This is due in part to their elongated hind legs. The other thing that helps them is a rubbery structure made of cross-linked proteins, called resilin, tucked behind their hind legs.
The back legs push against this mass, compressing it so that when they are released the elasticity of the resilin gives the legs an added boost. This jumping ability serves not only as a way of making a sudden escape but can also be used to jump up onto a host as it passes by.
How Fleas Develop
Female fleas lay eggs that fall off the host animal and develop on the ground into legless larvae that resemble tiny caterpillars, where they feed on the waste produced by adult fleas. Mammals that live in dens or nests are ideal for fleas because the larvae get plenty of food when the adult fleas can feed on animals that remain in the same location for many days at a time.
To complete their development, the larvae form a cocoon from sticky silk that they produce in their mandibular glands. Dirt sticks to the silk and helps the cocoons to remain camouflaged until the adult flea emerges, ready to find a host to get its first blood meal.
Common Questions about Dung Beetles and Fleas
When cattle were introduced to Australia beginning in the late 18th century, the native dung beetles could not process the large, wet patties made by the introduced cattle. The solution was to import dung beetles from other parts of the world that were better equipped to bury and consume cattle waste.
Fleas can jump the equivalent of 66 times their body length. This jumping ability serves not only as a way of making a sudden escape but can also be used to jump up onto a host as it passes by.
Fleas have bodies that are flattened from side to side. This compressed body, along with a reinforced exoskeleton, makes it very difficult to squish a flea.
