The general term “foxtail” refers to the barbed seed heads of several different grass species commonly found across California. This shared name describes a widespread concern, especially among pet owners who recognize the danger these plants pose. The distinct, brush-like appearance of the reproductive structure gives the plant its common name, yet this appearance masks a significant biological hazard. These grasses cause annual distress once the green growth begins to dry out.
The Definitive Answer: Status in California
The foxtail grasses that cause the most widespread problems in California are non-native, invasive species. The most common problematic species belong primarily to the genus Hordeum, particularly Hordeum murinum (Wall Barley or Hare Barley), and some species of Bromus (Brome Grasses). These plants originated predominantly in the Mediterranean region, Europe, and parts of temperate Asia.
The introduction of these plants to California was largely accidental, occurring during the state’s early settlement periods. Seeds traveled inadvertently alongside imported agricultural goods, livestock feed, or via contaminated ship ballast during the Spanish colonial and Gold Rush eras. Their establishment was swift, allowing them to rapidly colonize disturbed landscapes across the state. Their non-native status means they lack natural predators and diseases in California, contributing to their extensive spread.
Identifying the Problematic Grasses
The danger from foxtail grasses is not the plant itself, but the specific structure of its dried seed head, known as the awn. These awns are stiff, sharp bristles resembling a miniature arrow. The hazard lies in the microscopic barbs that cover the awns, which are aligned to permit movement only in a forward direction.
The grass is green and relatively harmless during the spring, but the risk begins in late spring and early summer when the plant dries out and turns brittle. Once dry, the spikelets easily detach from the main stalk and shatter into individual, barbed segments. These detached awns are lightweight and readily latch onto fur, clothing, or skin, making recognition of the dry grass patches a necessary preventative measure.
Ecological Success: Why Foxtails Thrive
The prevalence of these non-native foxtails is rooted in their adaptation to California’s Mediterranean climate. Species like Hordeum murinum function as winter annuals. They germinate with the first autumn rains, grow vigorously through the winter, and complete their entire life cycle before the dry summer heat. This quick life cycle allows them to produce seeds before many native perennial grasses have fully emerged.
These grasses thrive particularly well in disturbed, open areas like roadsides, vacant lots, and grazed fields. Their ability to tolerate a range of soils and their rapid growth rate allow them to outcompete native California grasses for resources. The barbed awns serve as an effective dispersal mechanism, easily catching a ride on passing animals, which aids in propagating the plant across new territories.
The Primary Health Risk
The microscopic barbs on the foxtail awns make them a mechanical hazard, especially for animals like dogs. Once an awn contacts fur or skin, movement causes the barbs to ratchet the awn deeper, preventing it from backing out. This makes the foxtail seed a one-way traveler capable of burrowing into soft tissue.
Common points of entry include the ears, where they cause head shaking, and the paws, where they embed between the toes, leading to licking and swelling. Awns inhaled through the nose cause persistent sneezing and discharge. In serious cases, they can migrate to the lungs or the cranial vault.
The seeds carry bacteria, and because the plant material does not break down inside the body, the migrating awn can cause inflammation, abscesses, and infection. If not removed promptly, the continued migration of the awn can lead to complications requiring surgery.