Here are some photos of Josh Esposito doing mosquito control in the backcountry near Bear Valley. The vernal pools can sometimes hold tens of thousands of mosquito larvae. Cattle are trucked up for spring and summer grazing, and provide unlimited blood for the snow pool mosquitoes. But years of treating have cut the mosquito numbers way down. (Note that we have not seen any negative impact on the frog population.)

Josh Esposito sampling for snow pool mosquito larvae at one of the numerous vernal pools in the Bear Valley area.

On far right you can see Josh as he samples the vernal pool for mosquito larvae.

Josh Esposito sampling for mosquito larvae at a vernal pool near Bear Valley California.

Josh Esposito sampling for mosquito larvae at a vernal pool near Bear Valley California.

Check out the highly twisted tree. Life is hard in the high mountains, even for the trees.

Don’t swim in that lake! It is not a lake. Josh Esposito poses in front if the Bear Valley Sewage Treatment pond.

The area around Columbia State Park was hydraulically mined during the gold rush, and many dug-out areas remain. These fill with water during the winter, becoming vernal pools. Floodwater mosquitoes like these pools.

Here are photos and videos showing how infested these pools can become. Included below is a compilation of mosquitoes suffocating videos, after a treatment with the BVA 2 oil.

11 May 2017.

Mosquito larvae in dipper cup, Columbia California, 11 May 2017.

Vernal pool (probably remains of hydraulic mining) loaded with larvae of floodwater mosquitoes. 11 May 2017.

Vernal pool (probably remains of hydraulic mining) loaded with larvae of floodwater mosquitoes. 11 May 2017.

For a number of years, the area around the homes located at the upper end of Apple Valley Drive, Sonora, California, have had extraordinary numbers of large, floodwater mosquitoes, genus Aedes (or Ochlerotatus), in the spring. These mosquitoes are larger than the western treehole mosquitoes that are common in the foothills at that time of year. The source of the floodwater mosquitoes has been a mystery, as searching in late spring did not reveal a source. We did a search in mid-April 2017, and found a major breeding area.

Hiking behind the creek, and towards Summer’s Pond, revealed a number of possibilities. Sampling yielded no mosquitoes, except in one location, at what appeared to be a small vernal pool on the edge of thick vegetation (1st photo below). About 100 feet away was what appeared to a second, small vernal pool (2nd photo below). The density of the brush and trees was so great that visibility was highly limited, and these pools did not appear connected. Further investigation revealed that the vegetation was concealing what was actually a gigantic vernal pool, about a quarter of an acre, its perimeter, and center as well, overgrown with thick vegetation. This cryptic, huge pool, hiding in plain sight, contained thousands of mosquito larvae.

The location of the pool is not discernable in the Google Earth 2016 satellite image (38°00’16.49″ N 120°19’32.67″ W), below, but is readily visible in the 1993 image, prior to the tree and shrub growth.

As we do elsewhere, we monitored the frogs, before and after treatment with the mosquito larvicidal oil, and found that the frog population was unaffected.

In addition, we explored a second potential mosquito breeding site, shown in the 1993 satellite image below, by the oval. Sampling on 23 April 2017 did not yield any mosquito larvae, but a number of the larger, floodwater mosquitoes were in the brush area, attempting to bite. This area appears to be directly linked to Summer’s Pond, and is also heavily overgrown. See the images below.

This trail goes between two thick brush areas. One edge of the large, cryptic vernal pool is on the right side of the trail, mostly under the brush.

What appears to be a separate, second vernal pool.

Arrow points towards the heavy growth that conceals the vernal pool.

This 1993 satellite image shows the area prior to the tree and shrub growth. The dark area, pointed to by the arrow, is the location of the vernal pool.

The oval shows another location that is probably a mosquito breeding area.

Swamp-like conditions adjacent to Summer’s Pond, in area enclosed by red oval on 1993 satellite image.

Swamp-like conditions adjacent to Summer’s Pond, in area enclosed by red oval on 1993 satellite image.

Photos taken on 31 May 2016. Click to enlarge.

Pollywogs of Sierra tree frogs in pond in Bloods Meadow, Bear Valley California. Note that these pollywogs were unaffected by mosquito larviciding.

The creek on the east end of Bloods Meadow has eroded this section of the meadow, leaving a precarious overhang. I presume a cow, grazing here in a few weeks, will discover that the ground will give way.

The pond in Blood’s Meadow.

The pond in Bloods Meadow harbors a lot of mosquito larvae, as well as Sierra Tree frogs.

The pond in Bloods Meadow.

Flowers blooming in Bloods Meadow.

Mosquito Lake, in Alpine County, is located a few miles east of Lake Alpine and Bear Valley. You might think, based on the name, that the mosquitoes are breeding in the lake. No, the mosquitoes come from vernal pools, or snow-melt pools, near the lake. These photos were taken 31 May 2016.

Click on an image to enlarge it.

Mosquito Lake, Alpine County, 31 May 2016. The mosquitoes do not breed in the lake, despite the name. (Note there are two ducks swimming in the lake. )

This vernal pool, near the western end of Mosquito lake, is only a few feet from Highway 4. This section had a high density of snow pool mosquitoes.

This same vernal pool, looking from a different direction, is adjacent to camping sites and a bathroom. This pool contained thousands of mosquito larvae.

This vernal pool, rather large, had a much lower density of mosquito larvae. It is also located across from Mosquito lake, adjacent to camping and picnic areas.

Another view of the larger vernal pool.

In this third image of the larger vernal pool, the heaviest density of snow pool mosquitoes was located at the far end.

These photos were taken May 24, 2016, at Bear Valley, near Blood’s Meadow.

Click to enlarge.

Vernal Pool, 24 May 2016, Bear Valley Ca, in the vicinity of the “Granite Staircase formation”. This pool is a breeding site for snow pool mosquitoes.

View from opposite side of the vernal Pool in the vicinity of the “Granite Staircase formation”. This pool is a breeding site for snow pool mosquitoes. 24 May 2016, Bear Valley Ca

This very large vernal pool is out beyond the Granite Staircase formation. 24 May 2016. It harbored just a relative few mosquito larvae.

Another view of the very large vernal pool beyond the Granite Staircase formation. 24 May 2016.

Remnants of old construction near the top of the Granite Staircase formation at Bear Valley. 24 May 2016.

The Granite Staircase formation, just before Bear Valley, coming from Calaveras County.

Another view of the Granite Staircase formation, just before Bear Valley, coming from Calaveras County.

This small pool had mosquito larvae in it. 24 May 2016.

(Note:click on an image to enlarge it)

T-Pool

Some snow melt pools, or vernal pools, can contain tens of thousands of mosquito larvae.  These photos and videos were taken on 30 March 2015, Alpine County. “T-pool” is named for being the top of  a “T’, coming up from ‘Fairy Shrimp Pool’ (see below).

“T-pool” Bear Valley Ca
March 30, 2015

“T-pool” Bear Valley Ca
March 30, 2015

“T-pool” Bear Valley Ca
March 30, 2015

“T-pool” Bear Valley Ca
March 30, 2015

Fairy Shrimp Pool

Views of Fairy Shrimp Pond, from both ends. This vernal pool is home to a species of fairy shrimp, as well as a lot of snow pool mosquitoes.

Fairy Shrimp pool. You can see a layer of ice covering the nearest portion of the pool. 2 April 2015

Fairy Shrimp pool. 2 April 2015

Fairy Shrimp 2 April 2015

Fairy Shrimp. 2 April 2015

The fairy shrimp species is probably Streptocephalus sealii, as it matches the description and distribution. This distribution map is from Fairy Shrimps Of California’s Puddles, Pools, And Playas  by Clyde H. Eriksen and Denton Belk, 1999.

Distribution of Streptocephalus sealii

Esposito Pool

This vernal pool contains surprisingly few mosquito larvae, despite its large size, and this rarity of mosquitoes occurs year to year.

Looking down the length of Esposito Pool. 2 April 2015

A portion of Esposito Pool. 2 April 2015

Ice on part of Esposito Pool. 2 April 2015

Esposito Pool. 2 April 2015

Bloods Meadow Pool

Bloods Meadow is home to a very large vernal pool in early spring. We find mosquito larvae all around its fringes, and in various locations within the meadow itself.

Bloods Meadow vernal pond 2 April 2015

Sierran Treefrog – Pseudacris sierra is common near Bloods Meadow pool.

Sierran Treefrog lives near the vernal pool in Bloods Meadow. 2 April 2015