Beetles

We see them in the garden frequently, but what makes a beetle a beetle?

Beneficial soldier beetle (UCANR)

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​Entomologists estimate that there are 400,000 - 1,000,000 species of beetle in the world. Beetles make up 40% of all insects and 25% of all life forms! They are members of the Coleoptera order. That name comes from Greek words that mean “sheathed wing”. The word beetle comes from the Old English word bitula, which means 'to bite'. Fossil records show that beetles have been around for 300 million years.

Adult spotted cucumber beetle (UM Extension)

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Beetle anatomy

Basic beetle anatomy has stayed relatively the same since their prehistoric beginnings. [If it ain’t broke, why fix it - right?] Like most insects, they have three major body parts (head, thorax, abdomen), antenna, wings, compound eyes, and protruding jaws. They are protected by an especially hard exoskeleton made up of plates called sclerites and they have claws on the lower segment (tarsi) of each leg.

    Wings - Most beetles have two pairs of wings. The front pair have evolved into hardened shell coverings called elytra. The back pair are used for flying. (Some species have lost the ability to fly.)
    Jaws - Beetle jaws (mandibles) move side-to-side, rather than up and down. Generally, males have more elongated mandibles than females. 
    Eyes - All beetles have compound eyes, which means their eyes are made up of many viewing screens. Among insects, honeybees are considered to have pretty good vision at 1/60. [What we can see from 60 feet away, a bee could only see 1 foot away] What they lack in vision, they more than make up for with adaptability and resilience. For example, aquatic whirligig beetles have split eyes that allow them to see both above and below the waterline!
    Antenna - A beetle’s segmented antenna are used to smell things and to feel around.

Lady beetle (Giles San Martin)

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Beetle lifecycle

Beetles are found everywhere on earth except for the polar ice caps. They go through distinct developmental stages that look very different from other stages. This is called complete metamorphosis. They start out as eggs that hatch into larvae. Beetle larvae eat a lot! Then they enter a resting pupal stage, where they are transformed into an adult beetle. Beetles tend to be very territorial and mating rituals are particularly brutal. Burying beetles wage war against their neighbors until only one male and one female are left to reproduce, ensuring the strength and fitness of there local gene pool. A female beetle may lay as many as several thousand eggs in her lifetime. Most species abandon the eggs as soon as they are laid, while a few create nurturing habitats for their young and stick around to protect the eggs from predators.


Beetle communication​

Beetles use chemicals called pheromones to communicate and to seek out mates. The aggregative pheromone calls other to a feeding site, while the anti-aggregative pheromone tells others to stay away. Some beetle species use a scraper on their abdomen to make sounds that are not audible to us humans. Pheromone traps, strong winds, and loud noises can really mess up a beetle’s romantic intentions.

Adult Colorado potato beetle (UM Extension)

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Feeding habits of beetles​

Most beetles prefer eating dead plant material and dung. Many beetles are host-specific, which means they have favorite foods, and some are omnivores, eating plants, earthworms and snails. There are only a few predatory beetles and a handful that prefer carrion.


Beetle defense

Beetles use camouflage, toxicity, mimicry and active defense measures to stay alive. Some species look like bird poop, while others look too much like wasps for predators to give them a taste. Other species use color to blend into the scenery. They can also secrete chemicals that make themselves taste bad. Some of these chemicals also provide protection against microbes. Very often, beetles get these chemicals from the plants they eat. Some species can spray these chemicals with surprising accuracy! Larger beetles have horns or spines, used to attack would-be predators.


Beetles as pollinators

While not significant pollinators, beetles are generally attracted to large, flattened or cup-shaped off-white or green flowers, such as dill, carrot, and other umbellifers, or those with heavy scents similar to decaying matter.


Beetles as pests
Since larval beetles tend to feed voraciously on agricultural crops, they are mostly considered pests. According to a study by Mississippi State University, the boll weevil came into the U.S. from Mexico in 1892. Traveling an average of 100 miles a year, this little beetle has cost the cotton industry an estimated $13 billion! Beetles are also responsible for destroying American elm populations because they can carry Dutch Elm Disease.

These are some common beetles found in the garden:

• Lady beetle
  
• Colorado potato beetle (a huge pest that has become resistant to most pesticides)
• Ground beetle (feed on fly eggs, caterpillars and other pests)
  Rose curculio (feeding causes ragged blossoms)
• Bean weevil
• Pea leaf weevil (chews notches on leaves and can kill seedlings)
• Cucumber beetle
• Wireworms (orange cylindrical larvae feed on roots and new shoots)
• Green fruit beetle (adults feed on ripe fruit)
• Soldier beetle (this highly beneficial predator loves to eat aphids and they pollinate flowers!) 

So, beetles can be good or bad, from a gardener’s perspective. Take a stroll through your garden and see what’s crawling (or flying) around!