A red and white spider with horns is likely to be either a spiny-backed orb weaver or an arrowhead orb weaver. Both spiders are similar in size and behavior, but they look very different. They also tend to live in shrubs or low trees, especially near water.
Observe the spider web
Both types of spiders spin webs to catch their prey. However, the spiny-backed orb weaver adds tufts of silk to the web that serve as warnings to birds to prevent damage to the web. Arrowhead orb weavers spin a standard web.
Look at the shape
The spiny-backed orb weaver is wider than it is long, ranging from 0.4 to 0.5 inches in width, but only 0.2 inches to 0.35 inches in length. The arrowhead gets its name from its triangular shape. They are approximately 0.37 inches long. The spiny-backed orb weaver has six red spines, or horns, around the perimeter of its abdomen. The arrowhead has two red spikes protruding from the back of the abdomen.
Examine the coloring
Both spiders come in a range of colors. The spiny-backed orb weaver typically has a white abdomen with black dots and red spines, while the arrowhead has a white-yellow abdomen with black spots. The horns are red at the roots and black at the tips.