Polyphylla decemlineata
In 3 days ~10% in a week ~30%
The ten-lined June beetle (Polyphylla decemlineata), also known as the watermelon beetle, is a scarab beetle found in the western United States and Canada. The adults are attracted to light and feed on foliage, notably mature pine needles. They can make a hissing sound when touched or otherwise disturbed, which can resemble the hissing of a bat. This sound is made by their wings pushing down, forcing the air out between their wings and back. They can be an agricultural pest affecting a wide range of crops because their larvae feed on plant roots and can weaken or kill the plants.
They are relatively large in size, some growing to sizes as large as 1.5 inches (3 cm) or more. As in other members of this genus, the males have large distinctive antennae consisting of several lamellate plates, which they close up when threatened. The antennae are used to detect pheromones emitted by the females. The wing covers (elytra) have four long white stripes and one short stripe each. The underside of the thorax is covered with brownish hairs.
This species is commonly confused with Polyphylla crinita, also known as the Long Haired June Beetle. Polyphylla decemlineata... Wikipedia →
| # | Park | Country | Daily sighting probability |
|---|---|---|---|
| 1 | Zion National Park | 🇺🇸 United States | |
| 2 | Yellowstone National Park | 🇺🇸 United States | |
| 3 | Yosemite National Park | 🇺🇸 United States |
| # | City | Country | Daily sighting probability |
|---|---|---|---|
| 1 | Salt Lake City | 🇺🇸 United States | |
| 2 | Denver | 🇺🇸 United States | |
| 3 | San Diego | 🇺🇸 United States | |
| 4 | Portland | 🇺🇸 United States | |
| 5 | Sacramento | 🇺🇸 United States | |
| 6 | Los Angeles | 🇺🇸 United States | |
| 7 | Seattle | 🇺🇸 United States | |
| 8 | Austin | 🇺🇸 United States | |
| 9 | San Francisco | 🇺🇸 United States |
Rare
Under 5% of wildlife watchers report a Ten-Lined June Beetle sighting in Yosemite National Park on a given day, based on 5 verified sightings from GBIF citizen-science data from 2019 to 2026. It is the 192nd most-seen of the 227 insects we can rate there. Over three days the chance rises to about 10%, and over a week to about 30%, if each day is a fresh chance.
July
In that month about 10% of wildlife watchers report a Ten-Lined June Beetle in Yosemite National Park on a given day, against under 5% in August to June, the lowest months. That is one of Yosemite National Park's driest months, with about 25 mm of rain against 220 mm in January.
Between 2 and 5 pm
Across all the parks we cover, that three-hour window holds the most Ten-Lined June Beetle sightings with a recorded time, and about 6 in 10 of them come between 6 am and 6 pm: it is seen both by day and at night.
3rd of 3
Of the 3 parks where we can rate Ten-Lined June Beetle sightings, Yosemite National Park ranks 3rd at under 5%. The best odds are in Zion National Park (United States, about 10%) and Yellowstone National Park (United States, under 5%).
GBIF citizen-science records
It is estimated from how often the Ten-Lined June Beetle is recorded against all the insects logged in Yosemite National Park (5 verified sightings from 2019 to 2026), calibrated against known sighting rates. Figures are rounded to the nearest 10% because citizen-science data supports honest approximations, not decimals, and months with records from fewer than five people show "—". How it works.
