August EcoFlora Challenge | Monsoon Soon | Desert Botanical Garden


Join the August EcoQuest: Monsoon Soon

Help find and map species that are associated with monsoon season.

It’s safe to say that rain is long overdue here in metro Phoenix. When you think about monsoon season, what comes to mind? Maybe the smell of rain or the sound of toads? How about bugs or even toppled trees? For this month’s EcoQuest, take the time to investigate a few Sonoran Desert species that are associated with monsoon season.

Wander your neighborhood to see what you find, hopefully after a much-needed rain. Share your favorite monsoon season blooms or creatures.

Join the EcoQuest here:

Observation Guide to help identify these plants, animals and insects:

There are two rainy seasons in the Sonoran Desert, one in winter, bringing somewhat regular and gentler storms, and one in summer with heavier and sporadic storms. The summer rains are known as monsoon season, and this is said to be around June through September. Monsoon season can bring half the annual rainfall for the year-sometimes in a single storm. These rains follow the hottest and driest season, and they are critical for the plants, animals and insects that depend on this cyclical rainy relief.

In modern urban society the harshness of the desert can be downplayed. Homes, air conditioning and a consistent water source keep many people safe from the extreme desert temperatures. Those that are without these comforts experience the immense relief that monsoon season can bring in a powerful way. Monsoon rains bring life to the Sonoran Desert, and humans are connected to this season too. The human nose can detect chemical components from the smell of rain in very low concentrations -about 5 parts per trillion. It is thought that this is because of humans’ reliance on water and rainy seasons for survival. Monsoon season recharges groundwater aquifers and provides water for drinking and for agriculture. Learning about monsoon season and the life sustained by it helps us recognize its importance for the ecosystem and people.



Creosote (Larrea tridentata)
When it comes to monsoon season, there is one plant in metro Phoenix that seems to stand out in many people’s minds. That plant is creosote, and it is the main plant responsible for the smell that comes with monsoon rains. The “after-rain smell” is known as petrichor, and it’s a bit complicated to explain. The word petrichor has its origins in Greek, meaning “stone” and “the fluid that flows in the veins of the gods.” This smell is a mix of plant oils (like creosote) and geosmin (a by-product of actinobacteria that can be found in the soil) that chemically interact when rain falls, especially in dry areas like deserts. Ozone can play a role in this smell too, if there is lightening. You don’t have to leave the city to experience this smell, thanks to the many creosote plants throughout metro Phoenix.

Arizona Spikemoss (Selaginella arizonica)
Rain is a life-giving force, especially in the desert. Arizona spikemoss can appear to not be alive at all. During hot dry periods, this plant can virtually blend in with the rock and soil around it, growing on shaded slopes and crevices. With monsoon rainfall, this plant makes a dramatic transformation, turning from dry brown to a lively green in a very short amount of time. This plant is sometimes referred to as “resurrection moss,” seemingly coming back to life.

Mesquite (Prosopis spp.)
Unfortunately toppled treed are often associated with monsoon season, specifically mesquite trees. Native mesquite trees (Prosopis velutina, Prosopis glandulosa, Prosopis pubescens) have evolved ways to cope with harsh desert conditions. Mesquite trees have shallow roots that collect surface water and a taproot that can access much deeper water sources. Mesquite taproots have been found growing 150 feet into the ground. This helps mesquite trees hold fast in monsoon storms.

Chilean mesquite (Prosopis chilensis) is not native to Arizona and tends to be more shallow rooted. When native mesquite trees are given frequent shallow watering, they can develop shallow roots as well. This can lead to the downed trees seen in monsoon storms. Planting native mesquites and watering them more deeply when needed can give these trees much better roots to hold on with and reduce the chance of toppling.

Palo Verde Beetle (Derobrachus germinates, Derobrachus hovorei)
They might be loud and look scary, but these beetles are basically harmless. They have the potential to bite, but only if very bothered and without much harm. Palo Verde beetles lay their eggs in the soil, the eggs hatch and the grubs can grow underground for two to four years. Grubs feed on, you guessed it, Palo Verde and other woody tree roots. The grubs are not considered a threat to healthy trees, instead normally feeding on older or stressed trees. The adult beetles emerge and start buzzing around the same time as the start of monsoon season. Adult beetles can be 3-4 inches in length and grubs can grow to 5 inches.

Desert Blonde Tarantula (Aphonopelma chalcodes)
During monsoon season nights and evenings male desert blonde tarantulas can be found wandering around in considerable numbers. Have no fear, these male tarantulas are simply out looking for a mate and eating insects that people consider pests along the way. They will not attack and will not bite unless aggressively handled or provoked. A city in California has been tracking tarantula activity for the past five years, and has found that rain reliably comes within six weeks of tarantula sightings.

Cicadas (Diceroprocta spp.)
The nearly deafening buzz of cicadas is a sure signifier of monsoon season. In fact, they are said to be the loudest insects in the Southwest. About four dozen species of cicada are thought to call Arizona home, and they can be nearly the size of a hummingbird to smaller than a quarter. You can hear cicadas being active even in the hottest weather, because they have figured out a way to “sweat” by releasing the liquids they consume from plants through small openings on their body.

Black Witch Moth (Ascalapha odorata)
Prompted by stormy weather, this moth can be seen during monsoon season in metro Phoenix while migrating, likely from Mexico. It flies mostly at night and has a reported wingspan of up to 7 inches. We may start seeing more and more of the Black Witch in our area. Researchers are looking to this moth for insight on climate change, as its migratory route moves ever further north.

Spadefoot Toad (Scaphiopus couchi)
Monsoon season is special for the Spadefoot toad. They spend a great deal of time resting underground and emerge almost exclusively during monsoon storms. It isn’t the moisture that cues them to emerge, but the vibration or low frequency sound from rain or thunder. Once they appear, they have one goal: making more Spadefoot toads in temporary pools and puddles. In a race to beat evaporation, tadpoles can sometimes grow to be young adults in as few as nine days. Listen carefully after a monsoon storm and see if you can hear their cat or sheep-like sounds.

Many plants have fruit or seed pods that ripen and are ready to harvest during monsoon season. To name a few:

Mesquite (Prosopis velutina, Prosopis glandulosa)

Palo Verde (Parkinsonia microphylla, Parkinsonia florida)

Prickly Pear (Opuntia spp.)

Desert Hackberry (Celtis pallida)

Some interesting monsoon season bloomers:

Devil’s Claw and Doubleclaw (Proboscidea althaeifolia, Proboscidea parviflora)

Desert Rosemallow (Hibiscus coulteri)

Arizona Poppy (Kallstroemia grandiflora)

Observing these plants and animals in metro Phoenix increases our understanding of how these Sonoran Desert species are connected to the monsoon season, and encourages us to explore our own connection, even in an urban setting.


Arizona-Sonora Desert Museum:

The University of Arizona:

Desert Harvesters:

Texas Butterfly Ranch:

The Tribune:

**PLEASE observe COVID-19 guidelines/recommendations.**
This a great opportunity to get outdoors close to home as we all navigate the complications of COVID-19. However, it is imperative that you follow the guidelines/recommendations of your local governments and institutions (wear a mask, practice physical distancing and wash your hands). Do what’s best for you and your community.

Arizona Office of Tourism: Responsible Recreation in AZ:

Please do not observe indoor houseplants or pets.

For your own safety and the protection of plants and wildlife, do not trespass when making observations. Please follow all posted rules and guidelines in parks/preserves and do not enter private property.

Do not remove or move natural materials (plants, animals, rocks).

Respect wildlife (do not touch, feed, or disturb animals and keep a safe distance).