Skip to content

Ixtapa Hermit Crab Med EarthCache

Hidden : 01/22/2007
1.5 out of 5
2 out of 5

Size: Size:   other (other)

Join now to view geocache location details. It's free!


How Geocaching Works

Please note Use of services is subject to the terms and conditions in our disclaimer.

Geocache Description:

This earthcache brings you to a little tide pool on the beach in Ixtapa along the Mexican Pacific coast. We found this tide pool while visiting Club Med Ixtapa, just a ¼ mile a way. The terrain varies with the tides, but it is fine for ages 5 and up.

There are many wonderful features of our Earth to observe at or around the tide pools at this cache. First, you should look at the beach itself, which is a beautiful example of one of the oldest described geologic features: a Beach cusp. Beach cusps are shoreline formations made up of various grades of sediment in an arc pattern. As you look down the beach, can you notice the humps of the beach cusp? Next, at the tide pools, you’ll see large rocks that demonstrate the historic and current volcanic activity of the region. Notice the large igneous formations. Now to the tide pool itself. What we were most intrigued by was both the variety of life and the way the population changes according to the tides. We visited this site several times. During high tide, there were sea snails everywhere. At low tide, the sea snails were out numbered by a vast community of hermit crabs. Why is this? Like all arthropods, hermit crabs have jointed limbs and segmented bodies. (Hermit crabs are actually decapods—they have 5 pairs of legs. The first pair is modified into claws and the last two pairs helps them hold onto the shell. The most common hermit crab in these tide pools are the Dwarf Red Tip Hermit Crab which has a red face and legs.) However, while great for moving about the tide pool, grabbing food and changing homes, hermit crabs' legs don't hang on to the rocks very securely. Sea snails on the other hand, don't have legs at all. They have special tongues called radulas, which help them to hold very tightly to the rocks of the tide pool. When high tide comes in, the hermit crabs get washed away or hide in cracks to avoid the stronger surf, but the sea snails use their radulas to hold fast to the rocks and ride out the waves. We were fascinated by this biological method of determining the tides. To log this cache, you need to: 1 Describe whether it is high tide or low tide. 2 Confirm whether it is high tide or low tide by determining the ratio of sea snails to hermit crabs —- you can do this by just selecting a sample pool and counting the number of both snails (tiny shells that don't move or move very slowly) and hermit crabs (shells that are moving around and have little red legs poking out). You won't have to pick them up to tell the difference if you are patient, so please be patient. Our observation (in January) was that in high tide sea snails out number hermit crabs by more than 2:1 and in low tide this ratio is reversed. What are your observations? You should write them in your log to here on to get credit for this cache. One final note: The number of available shells in the tide pool is very important to the survival of tide pool hermit crabs and can limit their numbers. So, please leave all seashells, even empty ones, in the tide pool where hermit crabs can reach them. To learn more about hermit crabs, see

Additional Hints (No hints available.)