Insects Active at night

Tile-horned Prionus

Prionus imbricornis

iNaturalist Wikipedia

A nocturnal giant with architecturally stunning antennae, the Tile-horned Prionus is one of North America's most impressive longhorn beetles. Often found near ancient oaks, these summer visitors bring a touch of prehistoric wonder to any backyard.

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Quick Identification

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Size

24-50 mm (0.9 to 2 inches) in length; males are generally smaller than females

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Colors

Uniformly dark reddish-brown to nearly black; shiny elytra (wing covers) with subtle punctures

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Key Features

16 to 20 overlapping, tile-like segments on antennae
Large, robust, and heavy-bodied appearance
Strong, forward-facing mandibles
Smooth, shiny wing covers with faint longitudinal ridges

When You’ll See Them

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Activity pattern Active at night

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Peak hours 9 PM - 2 AM

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Season June-August

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Diet Larvae eat the roots of living and dead hardwood trees (oaks, chestnuts, and fruit trees). Adults do not typically feed.

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Habitat Deciduous forests, orchards, and suburban areas with mature hardwood trees.

public Geographic range

Where Does the Tile-horned Prionus Live?

The Tile-horned Prionus is native to the North American continent, predominantly inhabiting the Eastern and Central United States. Its range extends from southern Canada and the Atlantic coast as far west as the Great Plains, reaching down through the Gulf States into Florida. Within this territory, it is most frequently encountered in areas with a high density of oak and chestnut trees, which serve as the primary hosts for its developing larvae.

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2 Countries

4.5M km² Range

Least Concern Conservation

US United States CA Canada

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iNaturalist / Verified observation data

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Behavior

The Tile-horned Prionus is a nocturnal longhorn beetle that spends the vast majority of its life cycle underground. As larvae, they are formidable root-feeders, tunneling through the root systems of various hardwood trees and shrubs for three or more years. When they finally emerge as adults during the mid-summer months, their primary focus shifts entirely to reproduction. Interestingly, adult beetles have a significantly reduced digestive system and rarely, if ever, feed, relying instead on energy reserves stored during their larval stage.

Adults are most active during warm, humid summer nights and are famously attracted to artificial light sources, which often leads them into suburban backyards. While their large size and powerful mandibles can be intimidating, they are not aggressive toward humans. However, they should be handled with care, as they can deliver a strong pinch if they feel threatened. Males are particularly active fliers, using their specialized, sensitive antennae to track the pheromones released by stationary females hidden in the leaf litter or near the base of trees.

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Camera Tips

Capturing the Tile-horned Prionus on camera requires a focus on nighttime photography. Because these beetles are strongly attracted to light (phototactic), the most effective way to photograph them is by setting up a 'light trap' within view of your camera. A simple white bedsheet hung vertically with a UV or mercury vapor light shining on it will often attract several individuals. Position your camera on a tripod at roughly eye level with the sheet, using a macro lens or a close-focus setting to capture the intricate details of their 'tiled' antennae.

If you prefer a more natural setting, place your camera near the base of mature oak trees or around old, decaying stumps in late June or July. Use a low-angle mount, such as a ground spike or a 'gorillapod' wrapped around a low branch, aiming the lens at the root flare where the trunk meets the soil. This is where females are most likely to be found and where males will land to search for them. Since these beetles move relatively slowly on the ground, a standard trail camera's trigger speed is usually sufficient, but high-sensitivity PIR settings are recommended due to the insect's cold-blooded nature.

For the best results, use a camera with a good external flash or an infrared (IR) setup that won't wash out the beetle's dark, shiny exterior. If using a standard trail camera, look for one with 'no-glow' IR to avoid overexposing the beetle's reflective elytra. Setting your camera to 'Burst Mode' can help you catch the moment they take flight, which involves a clumsy but fascinating unfolding of their large wings from beneath their wing covers. High-definition video mode (60fps) is also excellent for documenting the characteristic waving motion of their thick antennae as they navigate.

Similar Species

Species that look similar or are commonly confused with Tile-horned Prionus.

Broad-necked Root Borer

Has only 12-13 antennal segments and a much broader, more pronounced pronotum (neck area) compared to the Tile-horned Prionus.

California Root Borer

Found in Western North America; has thinner antennae and is generally larger and more elongated than the Tile-horned Prionus.

Hardwood Stump Borer

Light yellowish-brown with darker spots or bands on the elytra, unlike the solid dark brown of the Tile-horned Prionus.

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Frequently Asked Questions

Tile-horned Prionus beetles are strictly nocturnal. They are most active during the darkest hours of the night, typically from 9 PM until the early morning hours, especially during warm and humid summer nights in July and August.

The most effective way to attract them is by using light. They are highly attracted to bright porch lights, particularly those with a blue or UV spectrum. Maintaining mature hardwood trees like oaks also provides the necessary habitat for their underground larvae.

As adults, Tile-horned Prionus beetles rarely eat, living off stored energy. However, their larvae are 'root borers' that spend several years underground eating the roots of hardwood trees, including oaks, chestnuts, and various fruit trees.

Yes, they are quite common in suburban areas that have established landscapes and mature trees. Because they are attracted to artificial lights, they are frequently found on window screens, near porch lights, or on patio floors during the summer.

The key is the antennae. The Tile-horned Prionus (Prionus imbricornis) has 16 to 20 overlapping segments that look like roof tiles. The similar Broad-necked Root Borer usually has only 12 antennal segments and a noticeably wider 'neck' area.

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