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Why do Carpenter Bees Drill Holes?

Why do Carpenter Bees Drill Holes?

Carpenter bees, from the genus Xylocopa, are the largest native bee in the United States. They can be found across the southern and eastern United States. It is currently suggested that there are ~500 bees in this genus.

Unlike bumblebees and honeybees, carpenter bees do not live in colonies. Instead, they overwinter individually and mate in the spring, where the female will famously drill holes into hard plant material (i.e., dead wood, bamboo) to lay and feed the larvae – hence their name.

Why do Carpenter Bees Drill Holes?

As mentioned previously, female carpenter bees drill holes to lay their eggs after mating in the spring. The larvae, once hatched, will feed off pollen and nectar the female has stored for them until they are ready to forage in the late summer.

After they are done foraging for the season, carpenter bees will return to their tunnel to hibernate or die during winter. Although the carpenter bee’s behaviour is not entirely understood yet, it is commonly thought that only the mother, the father, and the female young will stay in a single nest.

After again mating in the spring, carpenter bees either clean out and enlarge old tunnels or create new ones as brooding chambers for their young.

How do Carpenter Bees Drill Holes?

Only female carpenter bees are known to drill holes, while males defend the nest.

Although steadfast and strong, a carpenter bee can only drill through ~1 inch of wood every 5-6 days. The female does so by using her mandibles to dig through the wood. The mandibles are two moveable jaws on the front of the bee’s face that allow her to cut through the wood in a small, circular motion. Instead of going up and down like human jaws, this set of jaws goes side to side.

At the beginning of building the nest, the female will dig a hole around 36mm straight into the wood– just big enough to get in and out. Once that original hole is about an inch deep, the bee will take a hard right turn and drill parallel to the wood’s surface.

From there, she will create burrowing “cells” with pollen and nectar for each of her larvae to live in and feed off until they are ready to forage. The female will continually discard the tiny bits of wood outside the hole or build them into partitions between each larvae’s cell throughout the process.

While the female is busy building the nest, the male will sit closely outside, waiting for predators or pests. If another insect or animal comes too close to the nest, the male will then hover around the intruder aggressively to make them go away. He uses his large and threatening presence to deter predators since, in fact, he doesn’t have a stinger to harm an intruder.

Once the female completes the drilling, she will seal up the nest – ensuring no predators get in. She will then leave for another nest while the larvae hatch and grow.

Identification

As there are around 500 subspecies of carpenter bees, they have numerous variations in their colorings. However, the five subspecies that are found in the U.S. share similar characteristics.

The carpenter bees found in the United States look very similar to bumblebees. Being around the same size and color, people often mistake one for the other. However, some notable differences will help differentiate one from the other.

First, these carpenter bees have shiny, smooth abdomens, while bumblebees have hairs along their entire body. Additionally, these carpenter bees have a solid black, sometimes iridescent abdomen, while bumblebee’s abdomens consist of a black and yellow striped pattern.

A carpenter bee on a succulent

Since the female is the only one that can sting, it is also worthy to note the differences between sexes. Male carpenter bees have a solid white color between their eyes, while the females do not. Other distinguishing features can be noticed in their behaviour, mainly whether they are drilling or defending the nest.

Damage

Luckily, carpenter bees don’t cause as much damage to property as other insects. The most significant damage is caused when the bees return to the same piece of wood year after year, creating numerous holes in the process. Additionally, the holes introduced by the carpenter bees can allow for moisture, rot, and decay to happen within the wood.

Once the eggs are in the nest, their scent and movement can also attract other woody pests, including woodpeckers. Once woodpeckers have spotted them, they will continue to expose and damage the wood surface.

Although males don’t sting, the presence of these large, loud bees can also be very intimidating.

Carpenter Bee Prevention

The best method of carpenter bee control is prevention. The best time for this is early fall when nests will likely be empty. Here are a few of the best ways to prevent carpenter bees from becoming pests at your property.

1. Cover Exposed Wood

Carpenter bees are drawn to weathered, untreated wood. The most susceptible spots around the house are windowsills, railings, decks, fences, doors, eaves, and wooden lawn furniture. Ensuring these areas of your home are painted or varnished will deter carpenter bees from drilling.

2. Avoid Certain Materials

Although not too specific, most carpenter bees prefer to use softer woods that allow for easier drilling. The woods most attractive to them are redwood, cedar, cypress, and pine.

3. Turn on Music

Most bee species communicate through vibrations and can hear low-frequency sounds up to 500 Hz. Because of this, bees can be deterred from an area if music is often played.

4. Hang a Decoy Wasp Nest

Since wasps are a more aggressive and territorial insect, most bees tend to avoid them. Hanging a decoy nest will cause carpenter bees to prevent nesting in that area.

You can find decoy wasp nests online, or you can make a DIY version by stuffing a paper bag with lightweight material and hanging it upside down.

Signs of Infestation

The most obvious sign of a carpenter bee infestation will be the ½- to ¾-inch circular openings in the wood. Since carpenter bees aren’t social, it is usually unlikely for there to be more than a couple of these holes.

If it is already late spring / early summer and the bee is active at work, there will also be signs of sawdust or wood shavings at the hole’s opening.

Lastly, if several males are hanging around one spot, it’s likely that a female and her nest are nearby. Alternatively, if there is one male aggressively hovering near you or your animals, you are probably close to their nesting site.

Control Methods

Luckily, there are plenty of conventional and non-conventional ways to treat carpenter bees. Here are a couple of ideas on how to get rid of these pesky insects:

1. Bee Trap

Bee traps essentially trick the carpenter bee into thinking the site will be good for a nest and trap them once inside. The trap consists of a wooden box with angled holes and a jar at the bottom.

The bees enter the holes in the wood, but because of how the light enters the box, they can only find the hole leading to the jar. There, they will eventually die. Once the jar is filled, you can unscrew it and discard the bees.

2. Bee “Dust”

Many types of insecticidal dust can be purchased and used to get rid of carpenter bees. To apply safely, treat the area at night. Because bees can’t see red light, it is also best to use a red-light headlamp to see what you’re doing.

Once the holes are located, apply the dust directly into the nest openings. It is crucial not to cover the hole at this point – if the bees don’t interact with the dust, they will create new exits from the tunnel.

Dust should be applied in spring when bees first emerge, mid-summer for any bees not killed during initial treatment, and early fall to kill any overwintering bees.

Some bee dust will not only kill adult bees living inside but will last long enough to kill any hatching larvae in the next mating cycle.

3. Cover Holes

Once it is ensured that the bees have exited the tunnel (usually by late summer), one of the best ways to ensure that they don’t return is by covering the holes. You can cover holes with caulk, a dowel, wadded aluminium foil, foam insulation, or steel wool. After covered, make sure to smooth the surface and paint or tarnish to avoid future infestation.

Conclusion

Carpenter bees are a genus of bees that drill holes in wood for laying their eggs. Females drill holes by using their mandibles to cut through the wood. The damage caused by carpenter bees is usually superficial but can allow for rot, fungi, and excessive moisture. Painting and treating wood is the best method of prevention. However, once an infestation has occurred, you can use a bee trap, bee dust, and covering holes as a way to control their presence.